I didn't want to send the user to a different page to manually activate the chosen plan upon, hopefully, a successful payment. To ensured minimal user interaction during purchasing and activation process, the frontend actively monitors the payment status by polling the backend. If successful, we automatically purchase the plan and activate it. Else redirect the user to the failed payment page.

Crediting and debiting the user's wallet is simple and easy to implement. But, it is not the best way to handle transactions within the system that requires to maintain wallet integrity and audit trail. For provision of audit trail, I added a ledger table that every user wallet should have. The ledger table records every transaction (interaction to add or deduct wallet balance) involving the user's wallet. For integrity, every addition or deduction of the wallet balance occurred inside a transaction.