The SSLCOMMERZ Sandbox API endpoint has been updated.
Old Endpoint:
https://sandbox.sslcommerz.com/gwprocess/v3/api.php
New Endpoint:
https://sandbox.sslcommerz.com/gwprocess/v4/api.php
Please update your integration accordingly and review the latest documentation on the developer portal: https://developer.sslcommerz.com/doc/v4/