How to organize the replenishment of the balance of users on the site?

Question

Payment systems

How can I organize the replenishment of the balance of ru-users on a self-written site (php)?
For example, if you just accept payments from users to one site account, then it’s more or less clear, but how can you make sure that each user can replenish their balance and spend on services on the site and that Wells billing is per user? Also through payment aggregators? Thank you!