Is it difficult to implement the described functionality for a programmer who has not worked with payment services at all?

Question

1C-Bitrix

Essence of the task:
Adding virtual goods with the possibility of replenishing the user's internal account when purchasing these goods. Placing an order with a minimum of actions, selecting a product and a button leading to a payment aggregator
You can use the internal account replenishment component. Payment is made through paypal. That is, the user must be able to replenish it so that in the future it can be used to pay for goods.

Answer 1

easy, PayPal has a developers sandbox