Hi Susanne,
Thanks for posting in the Community!
You can record an adjustment note to record the customer's credit. That way, the customer has an open credit and can use it to his future invoice. Here's how to:
- Click on the + New button.
- Select on Adjustment note.
- Fill out information like Customer name, email and in the products/service select the same product/item used in the original invoice.
- Enter amount.
- Click on Save and send.
Check this link to learn more about how to process customer refund in QBO.
Post again in the Community if you have further concerns about customer refunds.