Hello there, @fitzmiller! I'll help transfer the invoice credit.
In QuickBooks Online, you can create a journal entry to move an overpayment or credit from one customer to the other. I'll show you how.
Once done, apply the credit to the invoice in question accordingly. Here's an article you can read to learn more about transferring the amount of a customer's credit: How to Transfer a Credit from One Customer to Another in QuickBooks Online?
I've also included this helpful reference for the steps in creating a document showing all your customer sales activity and outstanding transactions: How to Send Statements to Show Customers Summaries in QuickBooks Online?
Don't hesitate to post a reply below if you have other questions or concerns with QuickBooks payments and credits. I'm always around happy to help. Stay safe and have a good one!
Joining this thread, fitzmiller. Allow me to help you apply a credit memo to your customer’s invoice in QuickBooks Online.
If a customer paid you more than what was owed, returning a product, requesting a refund you can create a Credit Memo. Once done, you can apply it to an open invoice for a given customer.
Step 1: Enter the credit memo:
Step 2: Apply the credit memo:
I'd recommend checking out this article: Create and apply credit memos or delayed credits in QuickBooks Online.
If your customer wants a refund, you can refer to this article for the complete guide: Record a customer refund in QuickBooks Online.
It would be my pleasure helping you further if you have additional concerns about invoices. Take care and have a great day!