Is it possible to bring forward an overpayment from a customer to qb online?

Yes, @paudieo.

We can record an overpayment in QuickBooks Online. I'll teach you how to do it.

Since you've mentioned that your customer doesn't want a refund, we can track them by creating a credit note. 

Here's how:

1. Select + New.
2. Select Credit Note.
3. In the Customer dropdown, select the customer's name.
4. Enter the details, such as the date and the amount. 
5. When you're done, choose Save and close.

After that, we can manually apply a credit note to an active invoice to your customer; follow the detailed steps in this article: Create and use credit notes or delayed credits in QuickBooks Online.

Moreover, we can quickly and easily review the status of sales transactions, open invoices, and generate sales data. See the complete detailed steps on this page: View sales transactions.

Hop again in this thread if there are things you want to know about your account. We are constantly right here to help. Happy holiday.