Hello, @AndrewC1.

You can use several payment methods in paying one invoice. Let me guide you how to do it.

1. Open the existing invoice.
2. Click the Receive Payments button.
3. From the Customer Payment window, make sure to review the customer's details.
4. Enter the payment amount you'll pay and specify its payment method.
5. Mark the Leave this as an underpayment radio button.
6. Click the Save and Close button. 

You can repeat the same process. Just make sure to select the correct payment method and amount when recording the payments. You can read through this article for more detailed steps: Use multiple payment methods towards an invoice.

Get back to us here if you have other questions. I'm always here to help.