Glad to have you here in the Community, @Ptonjalken.

We can delete the payments you've manually entered. This way, you can match the payment to the open invoice.

Here's how:

1. Go to the Sales menu, and then choose Customers.
2. Select the customer's name and proceed to the Transaction List tab.
3. Locate and click the payment to open it.
4. Click the More option at the bottom, and then choose Delete.
5. Select Yes to complete the process.

You can also check this article about managing your account register and utilize its related functions: Find, review, and edit transactions in account registers.

I've added this link in case you want to review your transactions after matching them: Find, Review, and Edit Transactions in your Account Register.

If there's anything else I can help you with, please let me know. I'll be around to help. Have a great day!