How do I set up auto apply credits to customers invoices?

We have to manually link the credit and the cheque you've created when refunding the customer, @Ldecaul. This will zero out the credit balance under the customer's record and remove it from the Accounts Receivable (AR) Reports. I'll guide you through applying this to close both entries.

To begin, let's ensure that Accounts Receivable (AR) is assigned to the cheque you've created for the refund. I've added a snapshot below for your reference:
 

Since your customer already has a credit in the records, we can start linking them using the steps below:
 

1. Click the + New icon and choose Receive Payments.
2. Select the customer with a credit and enter any additional information you have for the transaction.
3. Check the Cheque Expense entry under Outstanding Transactions and the Credit Note under Credits.
   
4. Click the Save and Close button to finish the process.

This process is performed manually because the option to automatically apply credits to customers' unpaid invoices is not available in the international version of QuickBooks Online.

Take a look at this article if you're interested in creating a recurring template for transactions that occur at regular intervals.

Feel free to reply to this thread if you have additional questions about managing customer credit or any QuickBooks-related matters. I'm always here to help. Take care!