@shayed here are some clarifications with an example.
Let’s say the payment system you have on your site are Paypal and Terawallet.
Now when a user tops up his wallet with $10, say via Paypal, $10 leaves his Paypal and goes in the PayPal account set up by the admin. A virtual $10 also goes to the user Wallet (So the user can see his bal as $10).
Now the real $10 is in admin’s Paypal account and a virtual $10 to be used for payments on your site is in the user’s account.
When the user makes a $10 purchase on your site and pays from his wallet, the virtual $10 leaves his wallet. No further action/entry is required as the $10 was always in admin’s PayPal account.
I hope this helps.