Changes to Create a payment request and return a payment_token for iframe flow

added the new optional request property webhook_endpoints

added the pattern ^[A-Za-z]{2}$ to the request property customer/country

added the pattern ^[A-Za-z]{3}$ to the request property order/currency

the error/code response's property type changed from string to no type for status 400

removed the optional property error/errors from the response with the 400 status

added the new optional request property billing_address

added the new optional request property merchant_id

added the new optional request property simulation

added the optional property error/metadata to the response with the 400 status

added subschema #1 subschema #2 to the error/code response property allOf list for the response status 400

endpoint added

api path removed without deprecation