Need to implement Backend POST Feature with payment

Hi there, I’m Drupal newbie, I need to use Commerce Ipay88 module, but the module seem abandoned and not complete, the coding almost like PayPal WPS module, everything is ok, payment success, except ipay88 need backend post/backend URL to be implemented,

Backend URL is a page at merchant server that act as secondary URL to receive SUCCESS payment status from ipay88 in case the Response URL fail to get notification. This page will not return to customer at front end.
Possibility of Response URL fail to get notification:
• Internet connection timeout/not stable on customer device thus iPay88 not able to return payment status to merchant response page after payment.
• Customer accidentally close web browser before payment cycle complete
• Customer device hang after the payment is processed thus iPay88 not able to return payment status to merchant response page.
• Bank delay response to ipay88 payment gateway.

Note
1. This Backend post feature will ONLY return status if the transaction is a payment success. No
status will return if the payment is failed.
2. The Backend page should implement checking same like response page such as signature
checking, and etc to prevent user hijack merchant system.
3. The backend page should not have session related code so that merchant systems are still able
accept payment status from iPay88 OPSG even if the user is logged out or the session is expired.
4. Ensure to implement a check to determine either "response page" or "backend page" to update
the order so it won't update order status in merchant system more than 1 time.
Note: After receiving the payment success status, iPay88 OPSG will simultaneously return
payment status to "response page" and "backend page".
5. The backend page is not a replacement for the response page. You will still need to continue to
use the normal response page as usual.

A correct backend URL implementation should return with response code '200' and Response Data 'Receive OK' (echo "RECEIVEOK";).
How do I need to implement this with Drupal Commerce Payment? Thanks.