Here is my code :

https://paiza.io/projects/SUiG5qp_wttfcrQn-0Mwew?language=php FYI -> [index.htm -> LineNo : 781 & 782]

After successfully received payment response page return 404 error

The form & CC-Avenue Payment Gateway Request page working good, after customer paid the response page return 404 error.

How can i solve the error?

Many online compilers and such block the app from doing much more than basic operations. You should put this on a real server that you know can access the URL from. Also, you need to vardump() the variables on the reticent line if you can't see why it's doing that.

Have you set the redirect-url correctly while setting up the payment gateway? as you mentioned 404, that means CCAvenue sent you successful payment response but is not under your control or something not defined.

I would recommend to use https://github.com/kishanio/CCAvenue-PHP-Library

Here in this library;

$ccavenue = new CCAvenueClient( '<merchant_id>', '<working_key>', '<redirect_url>' );

redirect_url should be the URL of your ccAvenueResponseHandler.php