Hello there, shabbaworld.
I can help you record your customers payments when a payment charge is involve in QuickBooks Online (QBO).
First, we can record the payment against the invoice for the full amount and ensure the Deposit To account is set to Undeposited Funds. You can refer to the screenshot below for your visual reference:

Once done, move the funds from the Undeposited Funds into your Bank account and deduct the sum-up charge at the same time. Here's how:
- Click +New and choose Bank deposit.
- Select the bank account where the money was deposited.
- Tick the customer payment you just recorded.
- From the Add funds to this deposit, choose an account (e.g. Bank Charges).
- In the Amount column, enter the fee as negative amount (-£0.88).

The total deposit amount at the bottom of the screen should now calculate to the net amount you actually received in your bank (£49.12). To double-check, you can go to the customer's profile and see if the invoice transaction is now in cleared.
For more details about depositing customer payments, check out this article: Record and make bank deposits in QuickBooks Online.
Please let me know if you still have concerns. I'd be glad to assist you.