When a customer pays for an additional charge in person (cash or card with you at the salon), you mark it as paid in the booking. That payment is recorded so the booking total and your revenue reports are correct, but the money goes directly to you—the platform never holds it. So that amount does not get added to your payout balance.
Only payments that go through the platform (e.g. when the customer pays online via Paystack for the same additional charge) are included in your payoutable balance. This way your balance always reflects money we are holding for you. Your finance page still shows "Walk-in add-ons" or similar so you can see total revenue including in-person sales.