How to record an instant transfer fee?

I'm glad to help record the charge so it will match with the payment you receive, Koko2.

Yes, you can change the invoice total by adding another line item for the transfer fee.

The fee should be negative to deduct the total amount and match it to the deposit. Here's a screenshot for your visual guide.

Also, make sure to use an expense account when tracking the transfer fee. That way, you can enter a negative amount. 

After editing the invoice, you can record the payment. Here's how;

1. Select + New, then Receive payment.
2. From the Customer drop-down, select the name of the customer.
3. From the Payment method drop-down, select the payment method.
4. From the Deposit to drop-down, select the account you put the payment into. 
5. In the Outstanding Transactions section, select the checkbox for the invoice you're recording the payment for.
6. Enter the Reference no. and Memo if needed. This is optional.
7. When you're done, click Save and close.

Once done, go to Banking page, then categorize and match the payment to the deposit. Here's a guide for you throughout the process: Categorize and match online bank transactions in QuickBooks Online.

Keep me posted if there's anything else you need about matching the invoice to the payment. I'll be right here to guide you.