Possible transaction statuses.

TRANSACTION_STATUS_UNSPECIFIED The status of the transaction is unspecified.
SUCCESS The transaction succeeded and details of the transaction are populated in transactionResponse.
INVALID_PLAN_ID The purchased plan ID is invalid.
PAYMENT_REQUIRED User does not have sufficient balance to complete the purchase.
CONFLICT The plan to be purchased is incompatible with the user's current product mix. For example, if the operator data plan policy disallows mixing postpaid and prepaid plans, attempting to purchase a prepaid plan for a postpaid user will therefore lead to a CONFLICT.