How to configure data exchange between STAMP server and website?

Question

PHP

Good day to all!
Dear experts, admins and developers, everyone is well aware of the general scheme of payment terminals.
I have such a situation, there is a terminal through which the user puts money, infa flies, for example, to the STAMP server further into the billing system, and so on.
After the user has deposited money by indicating his phone number, a certain account is opened.
I need to make a site with the help of which the user, after depositing money, was able to manage his own account, i.e. write off money to your card or transfer money to another user of the system.
So, the question is where should I dig to build this process?
Do I need to exchange data with this very STAMP server (Or any other) or do I somehow need to go directly to the billing system that manages all these money movements?
And by the way, the site will be on Bitrix, if it helps in some way.