Native checkout REST API implementation

This guide provides the technical API reference and payload schemas for version 2026-04-08 of the Universal Commerce Protocol (UCP) native checkout.

Before building your endpoints, ensure you have reviewed the Native checkout overview for the high-level checkout flow, authentication requirements, and developer tools.

Note: Google includes an Authorization: Bearer <access_token> header in requests to these endpoints. This is used for both machine-to-machine authentication and identity linking.

Create checkout session

This endpoint allows creation of a checkout session containing the products that a user is interested in buying.

• Endpoint: POST /checkout-sessions
• Trigger: User clicks "Buy now" on a product or "Checkout on Google" from the cart.

Request: Google sends the line items, and limited address information about the buyer, which includes city, state, and ZIP code.

// Request Example: Create checkout with multiple items.
{
  "line_items": [
    {
      "item": {
        // Must match ID in product feed
        "id": "product_12345"
      },
      "quantity": 1
    },
    {
      "item": {
        // Must match ID in product feed
        "id": "product_67890"
      },
      "quantity": 1
    }
  ],
  "context": {
    "language": "en-US"
  },
  "fulfillment": {
    "methods": [
      {
        "type": "shipping",
        "destinations": [
          {
            "address_locality": "Sunnyvale",
            "address_region": "CA",
            "postal_code": "94089",
            "address_country": "US"
          }
        ]
      }
    ]
  }
}

Response: You return the initialized session with totals, taxes (initially estimated), and payment capabilities.

Note: In the links array of the response, you must provide URLs for privacy_policy and terms_of_service. These two link types are required for display in the Google checkout UI.

Note on ucp.status field:

Introduced in version 2026-04-08, the ucp.status field indicates the creation outcome:

• "success" (or omitted): Default. Session created, even with recoverable messages.
• "error": Session creation failed due to an unrecoverable error (e.g., all items are out of stock). In this case, the response body should be an Error Response object, not a Checkout object. See the Unrecoverable Error example in the Error Handling section.

Note on totals array changes:

• The type field within each object in the totals array is now an open string.
• The amount field can now be negative (e.g., to represent discounts).
• Objects with type: "fee" can optionally include a lines array to itemize fee components.
• Tax-inclusive pricing: For tax-inclusive markets, the subtotal must include tax, the tax line item should be omitted, and display_text should be explicitly provided for subtotal and fulfillment entries in totals. See Tax-inclusive pricing for details.

// Response Example: Initialize Session with multiple items.
{
  "ucp": {
    "version": "2026-04-08",
    "status": "success",
    "capabilities": {
      "dev.ucp.shopping.checkout": [ { "version": "2026-04-08" } ],
      "dev.ucp.shopping.fulfillment": [ { "version": "2026-04-08", "extends": "dev.ucp.shopping.checkout" } ]
    },
    "payment_handlers": {
      "com.google.pay": [
        {
          "id": "8c9202bd-63cc-4241-8d24-d57ce69ea31c",
          "version": "2026-01-23",
          "spec": "https://pay.google.com/gp/p/ucp/2026-01-23/",
          "schema": "https://pay.google.com/gp/p/ucp/2026-01-23/schemas/config.json",
          "config": {
            "api_version": 2,
            "api_version_minor": 0,
            "environment": "TEST",
            "merchant_info": {
              "merchant_name": "Example Merchant",
              "merchant_id": "KWMZPRLQFTYNXSDB",
              "merchant_origin": "checkout.merchant.com"
            },
            "allowed_payment_methods": [
              {
                "type": "CARD",
                "parameters": {
                  "allowed_auth_methods": [ "PAN_ONLY" ],
                  "allowed_card_networks": [ "AMEX", "DISCOVER", "JCB", "MASTERCARD", "VISA" ],
                  "billing_address_required": true,
                  "billing_address_parameters": {
                    "format": "FULL",
                    "phone_number_required": true
                  }
                },
                "tokenization_specification": {
                  "type": "PAYMENT_GATEWAY",
                  "parameters": {
                    "gateway": "example",
                    "gatewayMerchantId": "exampleGatewayMerchantId"
                  }
                }
              }
            ]
          }
        }
      ]
    }
  },
  "id": "bf8c1b4b-6b1c-4c6a-8f2a-53c2a7c3b2e1",
  "status": "incomplete",
  "messages": [
    {
      "type": "error",
      "code": "missing_buyer_info",
      "path": "$.buyer",
      "content_type": "plain",
      "content": "Buyer information is required for checkout",
      "severity": "recoverable"
    },
    {
      "type": "error",
      "code": "missing_fulfillment_info",
      "path": "$.fulfillment.methods[0].destinations[0]",
      "content_type": "plain",
      "content": "Shipping address is incomplete",
      "severity": "recoverable"
    }
  ],
  "currency": "USD",
  "line_items": [
    {
      "id": "line_1",
      "item": {
        "id": "product_12345",
        "title": "Running Shoes",
        "price": 10000,
        "image_url": "https://merchant.example.com/images/product_12345.png"
      },
      "quantity": 1,
      "totals": [
        {
          "type": "subtotal",
          "amount": 10000
        },
        {
          "type": "total",
          "amount": 10000
        }
      ]
    },
    {
      "id": "line_2",
      "item": {
        "id": "product_67890",
        "title": "T-Shirt",
        "price": 2500,
        "image_url": "https://merchant.example.com/images/product_67890.png"
      },
      "quantity": 1,
      "totals": [
        {
          "type": "subtotal",
          "amount": 2500
        },
        {
          "type": "total",
          "amount": 2500
        }
      ]
    }
  ],
  "totals": [
    {
      "type": "subtotal",
      "display_text": "Subtotal", // Tax-inclusive markets: Set to "Subtotal (including taxes)".
      "amount": 12500 // Tax-inclusive markets: Amount must include tax.
    },
    {
      "type": "fee",
      "display_text": "Fees",
      "amount": 549,
      "lines": [
        { "display_text": "Service Fee", "amount": 399 },
        { "display_text": "Recycling Fee", "amount": 150 }
      ]
    },
    {
      "type": "fulfillment",
      "display_text": "Shipping", // Tax-inclusive markets: Provide display text for fulfillment totals.
      "amount": 0
    },
    {
      "type": "tax", // Tax-inclusive markets: Omit this entry.
      "display_text": "Estimated Tax",
      "amount": 1050
    },
    {
      "type": "total",
      "display_text": "Total",
      "amount": 14099
    }
  ],
  "fulfillment": {
    "methods": [
      {
        "id": "method1",
        "type": "shipping",
        "line_item_ids": [
          "line_1",
          "line_2"
        ],
        "destinations": [
          {
            "id": "addr_1",
            "address_locality": "Sunnyvale",
            "address_region": "CA",
            "postal_code": "94089",
            "address_country": "US"
          }
        ],
        "selected_destination_id": "addr_1",
        "groups": [
          {
            "id": "fg1",
            "line_item_ids": [
              "line_1",
              "line_2"
            ],
            "options": [
              {
                "id": "ship_ground",
                "title": "Ground (3-5 days)",
                "description": "Estimated Delivery: Fri 5/8", // Maximum length: 200 characters.
                "totals": [ {"type": "total", "amount": 500} ]
              },
              {
                "id": "ship_express",
                "title": "Express (1-2 days)",
                "description": "Estimated Delivery: Wed 5/6", // Maximum length: 200 characters.
                "totals": [ {"type": "total", "amount": 1500} ]
              }
            ],
            "selected_option_id": "ship_ground"
          }
        ]
      }
    ]
  },
  "links": [
    {
      "type": "terms_of_service",
      "url": "https://m.com/terms",
      "title": "Terms of Service"
    },
    {
      "type": "privacy_policy",
      "url": "https://m.com/privacy",
      "title": "Privacy Policy"
    }
  ]
}

Tax-inclusive pricing

For markets where tax is included in the displayed subtotal rather than itemized separately, your implementation must adhere to the following requirements when providing checkout session data:

• Include tax in the subtotal: The amount field for the subtotal entry must include all applicable taxes.
• Omit separate tax entries: Don't include a dedicated object with type: "tax" in the totals array.
• Provide custom display text: You must include a display_text attribute within the subtotal object that explicitly states taxes are included, such as "Subtotal (including taxes)". You must also include a display_text attribute for fulfillment entries (e.g. "Shipping").

Note: This approach ensures price transparency and aligns with regional expectations for cohesive order confirmation and detail screens.

Example: Tax-inclusive totals array

The following example demonstrates a totals array for a merchant in a tax-inclusive market:

"totals": [
  {
    "type": "subtotal",
    "display_text": "Subtotal (including taxes)",
    "amount": 12500
  },
  {
    "type": "fulfillment",
    "display_text": "Shipping",
    "amount": 399
  },
  {
    "type": "total",
    "display_text": "Total",
    "amount": 12899
  }
]

Get checkout session

This endpoint allows retrieval of a checkout session.

• Endpoint: GET /checkout-sessions/{id}

Request: Google sends the ID of the checkout session. If you use Global IDs (e.g., gid://merchant.example.com/Checkout/session_abc123), note that the ID in the request path will only be the last component of this ID (e.g., session_abc123).

Response: You return the full checkout object. For a multi-item session created under version 2026-01-23 or later, the line_items array will contain multiple item entries.

Update checkout session

This endpoint allows updates to a checkout session. When the shipping address is updated, it must recalculate and return taxes and shipping options.

• Endpoint: PUT /checkout-sessions/{id}

Update shipping address

• Trigger: User selects or changes their shipping address.

Request: Google updates the fulfillment address when the user changes their shipping address.

// Request Example: Update shipping address with multiple items.
{
  "line_items": [
    {
      // line_items id from Create Checkout response
      "id": "line_1",
      "item": {
        "id": "product_12345"
      },
      "quantity": 1
    },
    {
      // line_items id from Create Checkout response
      "id": "line_2",
      "item": {
        "id": "product_67890"
      },
      "quantity": 1
    }
  ],
  "context": {
    "language": "en-US"
  },
  "fulfillment": {
    "methods": [
      {
        "type": "shipping",
        "line_item_ids": [
          "line_1",
          "line_2"
        ],
        "destinations": [
          {
            "address_locality": "Mountain View",
            "address_region": "CA",
            "postal_code": "94043",
            "address_country": "US"
          }
        ],
        "groups": [
          {
            "id": "group1",
             "line_item_ids": [
              "line_1",
              "line_2"
            ],
            "options": [
              {
                "id": "ship_ground"
              }
            ],
            "selected_option_id": "ship_ground"
          }
        ]
      }
    ]
  }
}

Response: You recalculate taxes and shipping options as necessary and return the full checkout object.

// Response Example: Updated session with new address for multiple items.
{
  "id": "bf8c1b4b-6b1c-4c6a-8f2a-53c2a7c3b2e1",
  "currency": "USD",
  "line_items": [
    {
      "id": "line_1",
      "item": {
        "id": "product_12345",
        "title": "Running Shoes",
        "price": 10000,
        "image_url": "https://merchant.example.com/images/product_12345.png"
      },
      "quantity": 1,
      "totals": [
        { "type": "subtotal", "amount": 10000 },
        { "type": "total", "amount": 10000 }
      ]
    },
    {
      "id": "line_2",
      "item": {
        "id": "product_67890",
        "title": "T-Shirt",
        "price": 2500,
        "image_url": "https://merchant.example.com/images/product_67890.png"
      },
      "quantity": 1,
      "totals": [
        { "type": "subtotal", "amount": 2500 },
        { "type": "total", "amount": 2500 }
      ]
    }
  ],
  "totals": [
     { "type": "subtotal", "display_text": "Subtotal", "amount": 12500 },
     // Shipping cost might change based on new address
     { "type": "fulfillment", "display_text": "Ground Shipping", "amount": 600 },
     {
       "type": "fee",
       "display_text": "Fees",
       "amount": 549,
       "lines": [
         { "display_text": "Service Fee", "amount": 399 },
         { "display_text": "Recycling Fee", "amount": 150 }
       ]
     },
     // Tax will likely change based on new address
     { "type": "tax", "display_text": "Estimated Tax", "amount": 1120 },
     { "type": "total", "display_text": "Total", "amount": 14769 }
  ],
  "fulfillment": {
    "methods": [
      {
        "id": "method_shipping",
        "type": "shipping",
        "line_item_ids": ["line_1", "line_2"],
        "selected_destination_id": "addr_1",
        "destinations": [
          {
            "id": "addr_1",
            "address_locality": "Mountain View",
            "address_region": "CA",
            "postal_code": "94043",
            "address_country": "US"
          }
        ],
        "groups": [
          {
            "id": "group_1",
            "line_item_ids": ["line_1", "line_2"],
            "selected_option_id": "ship_ground",
            "options": [
              {
                "id": "ship_ground",
                "title": "Ground (3-5 days)",
                "description": "Estimated Delivery: Fri 5/8", // Maximum length: 200 characters.
                "totals": [ { "type": "total", "amount": 600 } ]
              },
              {
                "id": "ship_express",
                "title": "Express (1-2 days)",
                "description": "Estimated Delivery: Wed 5/6", // Maximum length: 200 characters.
                "totals": [ { "type": "total", "amount": 1600 } ]
              }
            ]
          }
        ]
      }
    ]
  }
  // ... other fields like ucp, status, messages, links
}

Full checkout object hydration

Request: Google sends the full checkout object with the updated information (including full fulfillment address and payment instrument) when the buyer clicks "Pay with GPay".

// Request Example: full checkout object hydration for multiple items.
{
  "buyer": {
    "first_name": "John",
    "last_name": "Buyer",
    "email": "[e-mail]",
    "phone_number": "[phone]"
  },
  "line_items": [
    {
      "id": "line_1",
      "item": { "id": "product_12345" },
      "quantity": 1
    },
    {
      "id": "line_2",
      "item": { "id": "product_67890" },
      "quantity": 1
    }
  ],
  "payment": {
    "instruments": [
      {
        "id": "gpay",
        "handler_id": "8c9202bd-63cc-4241-8d24-d57ce69ea31c",
        "type": "com.google.pay",
        "selected": true
      }
    ]
  },
  "context": {
    "language": "en-US"
  },
  "fulfillment": {
    "methods": [
      {
        "type": "shipping",
        "line_item_ids": ["line_1", "line_2"],
        "destinations": [
          {
            "id": "addr_1",
            "first_name": "Alice",
            "last_name": "Receiver",
            "street_address": "1600 Amphitheatre Pkwy",
            "extended_address": "Suite #60",
            "address_locality": "Mountain View",
            "address_region": "CA",
            "postal_code": "94043",
            "address_country": "US"
          }
        ],
        "groups": [
          {
            "id": "group_1",
             "line_item_ids": ["line_1", "line_2"],
            "options": [ { "id": "ship_ground" } ],
            "selected_option_id": "ship_ground"
          }
        ]
      }
    ]
  }
}

Response: You recalculate taxes and shipping options as necessary and return the full checkout object.

Note: Ensure that payment.instruments[0].handler_id exactly matches the id defined in your ucp.payment_handlers.com.google.pay configuration. A mismatch will result in an error for the customer.

// Response Example: Session after full hydration with multiple items.
{
  "ucp": {
    "version": "2026-04-08",
    "status": "success",
    "capabilities": {
      "dev.ucp.shopping.checkout": [ { "version": "2026-04-08" } ],
      "dev.ucp.shopping.fulfillment": [ { "version": "2026-04-08", "extends": "dev.ucp.shopping.checkout" } ]
    },
    "payment_handlers": {
      "com.google.pay": [
        {
          "id": "8c9202bd-63cc-4241-8d24-d57ce69ea31c",
          "version": "2026-01-23",
          "spec": "https://pay.google.com/gp/p/ucp/2026-01-23/",
          "schema": "https://pay.google.com/gp/p/ucp/2026-01-23/schemas/config.json",
          "config": {
            "api_version": 2,
            "api_version_minor": 0,
            "environment": "TEST",
            "merchant_info": {
              "merchant_name": "Example Merchant",
              "merchant_id": "KWMZPRLQFTYNXSDB",
              "merchant_origin": "checkout.merchant.com"
            },
            "allowed_payment_methods": [
              {
                "type": "CARD",
                "parameters": {
                  "allowed_auth_methods": [ "PAN_ONLY" ],
                  "allowed_card_networks": [ "AMEX", "DISCOVER", "JCB", "MASTERCARD", "VISA" ],
                  "billing_address_required": true,
                  "billing_address_parameters": {
                    "format": "FULL",
                    "phone_number_required": true
                  }
                },
                "tokenization_specification": {
                  "type": "PAYMENT_GATEWAY",
                  "parameters": {
                    "gateway": "example",
                    "gatewayMerchantId": "exampleGatewayMerchantId"
                  }
                }
              }
            ]
          }
        }
      ]
    }
  },
  "id": "bf8c1b4b-6b1c-4c6a-8f2a-53c2a7c3b2e1",
  "status": "ready_for_complete",
  "currency": "USD",
  "buyer": {
    "first_name": "John",
    "last_name": "Buyer",
    "email": "[e-mail]",
    "phone_number": "<REDACTED_PII>"
  },
  "line_items": [
    {
      "id": "line_1",
      "item": {
        "id": "product_12345",
        "title": "Running Shoes",
        "price": 10000,
        "image_url": "https://merchant.example.com/images/product_12345.png"
      },
      "quantity": 1,
      "totals": [
        { "type": "subtotal", "amount": 10000 },
        { "type": "total", "amount": 10000 }
      ]
    },
    {
      "id": "line_2",
      "item": {
        "id": "product_67890",
        "title": "T-Shirt",
        "price": 2500,
        "image_url": "https://merchant.example.com/images/product_67890.png"
      },
      "quantity": 1,
      "totals": [
        { "type": "subtotal", "amount": 2500 },
        { "type": "total", "amount": 2500 }
      ]
    }
  ],
  "totals": [
     { "type": "subtotal", "display_text": "Subtotal", "amount": 12500 },
     { "type": "fulfillment", "display_text": "Ground Shipping", "amount": 600 },
      {
        "type": "fee",
        "display_text": "Fees",
        "amount": 549,
        "lines": [
          { "display_text": "Service Fee", "amount": 399 },
          { "display_text": "Recycling Fee", "amount": 150 }
        ]
      },
     { "type": "tax", "display_text": "Estimated Tax", "amount": 1120 },
     { "type": "total", "display_text": "Total", "amount": 14769 }
  ],
  "payment": {
    "instruments": [
      {
        "id": "gpay",
        "handler_id": "8c9202bd-63cc-4241-8d24-d57ce69ea31c",
        "type": "com.google.pay",
        "selected": true
      }
    ]
  },
  "fulfillment": {
    "methods": [
      {
        "id": "method_shipping",
        "type": "shipping",
        "line_item_ids": ["line_1", "line_2"],
        "selected_destination_id": "addr_1",
        "destinations": [
          {
            "id": "addr_1",
            "first_name": "Alice",
            "last_name": "Receiver",
            "street_address": "1600 Amphitheatre Pkwy",
            "extended_address": "Suite #60",
            "address_locality": "Mountain View",
            "address_region": "CA",
            "postal_code": "94043",
            "address_country": "US"
          }
        ],
        "groups": [
          {
            "id": "group_1",
            "line_item_ids": ["line_1", "line_2"],
            "selected_option_id": "ship_ground",
            "options": [
              {
                "id": "ship_ground",
                "title": "Ground (3-5 days)",
                "description": "Estimated Delivery: Fri 5/8", // Maximum length: 200 characters.
                "totals": [ { "type": "total", "amount": 600 } ]
              },
              {
                "id": "ship_express",
                "title": "Express (1-2 days)",
                "description": "Estimated Delivery: Wed 5/6", // Maximum length: 200 characters.
                "totals": [ { "type": "total", "amount": 1600 } ]
              }
            ]
          }
        ]
      }
    ]
  },
  "links": [
    {
      "type": "terms_of_service",
      "url": "https://m.com/terms",
      "title": "Terms of Service"
    },
    {
      "type": "privacy_policy",
      "url": "https://m.com/privacy",
      "title": "Privacy Policy"
    }
  ]
}

Complete checkout session

This endpoint allows completing a checkout session and placing an order. It should return the completed checkout session and include the order information. Payment processing should begin after this call is received.

• Endpoint: POST /checkout-sessions/{id}/complete
• Trigger: User clicks "Pay with GPay", and Google receives a successful response from fully hydrated checkout update.

Request: Google sends the selected payment instrument from the payment handler including the credential (e.g. Google Pay tokenization data) and risk signals about the buyer for you to perform your own fraud detection. The token contents will depend on your Payments Service Provider.

{
  "payment": {
    "instruments": [
      {
        "billing_address": {
          "first_name": "John",
          "last_name": "Buyer",
          "street_address": "1600 Amphitheatre Pkwy",
          "address_locality": "Mountain View",
          "address_region": "CA",
          "postal_code": "94043",
          "address_country": "US"
        },
        "credential": {
          "token": "examplePaymentMethodToken",
          "type": "PAYMENT_GATEWAY"
        },
        "display": {
          "brand": "VISA",
          "description": "Visa •••• 1234",
          "last_digits": "1234"
        },
        "handler_id": "8c9202bd-63cc-4241-8d24-d57ce69ea31c",
        "id": "94e7fee0-1a82-4c2a-9ef4-0861a3c829b2",
        "selected": true,
        "type": "CARD"
      }
    ]
  },
  "signals": {} // Placeholder for risk signals
}

If you require mandatory information to complete checkout that has not been provided in the checkout session, you can prevent checkout completion and request that information by returning a non-complete status in the response.

If Google can collect the missing information using UCP-defined fields (for example, buyer's email address), set status to incomplete and include one or more messages in the messages array with severity set to recoverable, indicating what information is missing.

{
  "id": "da2e25ec-eef8-41b7-a439-4e62dea41bdc",
  "status": "incomplete",
  "messages": [
    {
      "type": "error",
      "code": "missing_buyer_info",
      "severity": "recoverable",
      "content": "Buyer email is required"
    },
    {
      "type": "error",
      "code": "missing_fulfillment_info",
      "severity": "recoverable",
      "content": "Select delivery window for your purchase"
    }
  ]
}

Upon receiving a Google Pay payment instrument, you must:

1. Validate handler: Confirm handler_id corresponds to the Google Pay payment handler.
2. Extract token: Retrieve the generated payment method token from payment_data.credential.token.
3. Process payment: Use the token and transaction details to complete payment. Refer to Google Pay API documentation for detailed documentation on tokenization specification and handling.

Response: If checkout can be completed and you have processed payment, you return the full checkout object indicating the order is complete, including the order ID and a permalink URL to the order.

{
  "ucp": {
      "version": "2026-04-08",
      "capabilities": [...]
  },
  "id": "da2e25ec-eef8-41b7-a439-4e62dea41bdc",
  "status": "completed",

  // ... other fields (line_items, currency, etc.)

  "order": {
    "id": "ORD1773956535.2727807",
    // Example customer-facing order number
    "label": "#100",
    "permalink_url": "https://merchant.example.com/orders/789"
  }
}

Cancel checkout session

This endpoint cancels a checkout session.

• Endpoint: POST /checkout-sessions/{id}/cancel

Request: Google sends the ID of the checkout session.

Response: You return the full checkout object with the status updated to canceled.

Error handling

For complete guidelines on how to format error messages and the distinction between protocol and business logic errors, see the Error codes overview.

Unrecoverable Error

Starting with version 2026-04-08, when an unrecoverable error prevents checkout session creation (e.g., all items are out of stock), return an HTTP 200 OK. In the response body, set "status": "error" within the ucp object. This tells Google the request was valid, but a business rule blocked session creation. No checkout session ID is returned in this case.

HTTP/1.1 200 OK
Content-Type: application/json

{
  "ucp": {
    "version": "2026-04-08",
    "status": "error"
  },
  "messages": [
    {
      "type": "error",
      "code": "out_of_stock",
      "content": "All requested items are currently out of stock",
      "severity": "unrecoverable"
    }
  ],
  "continue_url": "https://merchant.com/"
}