I can help you manage this transaction, @appliedcoatings.
Since the payment is deposited with a discount, you can create a credit memo to immediately reduce the customer's current balance. I’ll show you how:
- Click the + New button and select Credit memo.
- Choose the customer name.
- Fill in the necessary information.
- Select Save and close.
Once done, apply it to the customer’s invoice. Here’s how:
- Go to the Sales menu, then choose Invoices.
- Locate the customer’s transaction, then select Receive payment.
- In the Outstanding Transactions section, make sure that the correct invoice is selected.
- Ensure also the total is correct after applying the credit memo.
- Press Save and close.

I’ve attached a reference here on how to make deposits in QBO. This makes sure your records match your real-life bank deposits.
If you have additional questions with payments, please don't hesitate to leave a message in the comment section. We'll be happier to help you more. Take care and have a good one!