Secure payment service?

Question

PHP

Hello. I made one account for all my projects (php) As a result, I received one registration, etc. Now I have connected a payment aggregator to my office. (now there is a currency that needs to be transferred to other projects)
The essence of the question is how is it generally safe to do this? (all projects on different servers, etc.) Interested in what checks to do. (the code is not necessary, but only what checks to do and that's it)
ATP in advance

Answer 1

LK when replenishing the balance transfers real money to virtual.
Since you have one personal account for several projects, replenish through a command from the user, causing inter-server data exchange.
Bundle: service ID and amount (user ID, depends on the implementation, in theory - it is not needed with a centralized personal account)
Make access to replenishment only from the IP addresses of the platform personal account, you can also make a verification hash: md5 (salt + rnd +summ+timestamp+salt) and pass everything except salt in plain text via POST.
It is desirable to do everything through SSL and / or VPN.