Following HTTP Status Codes applicable to message response from payment gateway.

Status Code	Description
200	OK - Successful response for HTTP requests.
400	Bad Request – PG server rejects request from merchant due to : syntax error or insufficient request information (missing parameters) transaction amount less than minimum amount Invalid API version
401	Unauthorized – merchant request does not pass the PG authentication. Example scenarios such as an unregistered merchant server’s IP address trying to make a request to the PG server. Invalid application code. Duplicate referenceID.
404	Not found – Application code or transaction not found
500	Internal Server Error – Error occurred due to PG internal processing.
502	Bad Gateway – Error occurred on channel. Merchant required to inquiry to check/reversal.
504	Gateway timeout – timeout between PG server and channel. Merchant required inquiry to check/reversal.