> [!CAUTION]
> **Caution:** This documentation is for Google Ads API **v23** . The latest active version is [**v26**](https://developers.google.com/google-ads/api/reference/rpc/latest/ConversionCustomVariableOperation).

A single operation (create, update) on a conversion custom variable.

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v23/services/conversion_custom_variable_service.proto)

| Fields ||
|---|---|
| ## `operation` Union field. The mutate operation. `operation` can be only one of the following: ||
| ### `create` | `ConversionCustomVariable` Create operation: No resource name is expected for the new conversion custom variable. |
| ### `update` | `ConversionCustomVariable` Update operation: The conversion custom variable is expected to have a valid resource name. |
| ## `update_mask` | `FieldMask` FieldMask that determines which resource fields are modified in an update. |