Hello there, FineCarp.

You have to create a journal entry to offset your A/P account with your Clearing account, so you'll be able to clear the overpayment. Let me walk you through.

To create a clearing account, please refer to @Charies_M for the steps.

Then, create a journal entry. Here's how:

1. Click Create (+).
2. Click Journal Entry.
3. In the Account column, select Accounts Payable (A/P), enter the overpayment amount in the Credit column.
4. Click the vendor's name.
5. In the next line, select the Clearing Account, then enter the same amount in the Debit column.
6. Click Save.
7. Locate open transaction and click Make payment apply the journal entry.
8. Click Save and close.

Feel free to read this article for your reference: How to record a barter transaction.

The Community is always here for you if you have questions. Stay in touch.