PHP Programmer needed for API Payment Notification

We need hire/pay someone familiar with s2member and php.
We need PHP Webhook (aka: API Notification Handler) to update a S2member custom field on API payment notification.
All the php code will do is increment a custom field by 1 every time a payment notification comes in.
example:
custom field name is user_credit default is 0.

API payment notification triggers…
notification 1. user_credit =1
notification 2. user_credit = 2
notification 3. user_credit = 3
etc…

Anyone experienced in s2member and can tackle this, please let me know.

Thank you