How can I organize an internal account on the site?

Question

Java

Suppose there is a service, you need to organize the following functionality:
1) replenishment of the internal account of this service and payment, the possibility of paying from the internal account of payments
2) payment immediately from the real - at this point, which systems are better to use (Oplata.info?)
PS also need to withdraw money back to real from the account
are there any systems / solutions how to organize this, if not, how is it usually done?
- some kind of account is created ((on which all funds are stored) and all payments and withdrawals go to it?

Answer 1

A table is created in the database with the balance column tied to the user. And various operations are performed on it.
It is also desirable to create a table of transactions over this account.
Entering the withdrawal of money is already an integration task and it is necessary to consider a specific case.
Usually payment systems have an API