AddPay uses conventional HTTP response codes to indicate the success or failure of an API request. In general: Codes in the 2xx range indicate success. Codes in the 4xx range indicate an error that failed given the information provided (e.g., a required parameter was omitted, validation failed, etc.). Codes in the 5xx range indicate an error with our servers (these are rare).

These errors are in relation to general HTTP API request errors and are not associated with transaction status and/or transaction response errors, see the specific API reference article per resource endpoint for resource error status keys and codes.