Thanks for pointing me to this! Looks like the token will ONLY be available if the customer chooses to save it. For cases when the customer owes us money, we can just send them to the payment page to pay the remaining balance correct?

How do we handle the scenario where the customer changes an order prior to invoicing, and the resulting change creates a balance we owe them? After we create the invoice, I see no indication that they overpaid. I also don't see an option to refund them. I've been pulling my hair out on this one so any help you can provide would be much appreciated!

I have not tested your workflow. The Aged Receivable report shows Customer that you own money to. Documentation on refunds is at https://www.odoo.com/documentation/16.0/applications/finance/payment_providers.html#payment-providers-features-refund