We can record a credit note to your client, @estacare.
By creating a credit note, your client can use this as a payment to an invoice. I'll show you how:
Then, you can apply the credit note to an invoice. Here's how:
In case you need tips on how to record money you return to your customer, you can check this reference: Record a customer refund in QuickBooks Online.
Feel free to drop by anytime if you have queries in managing customer transactions in QBO. I'm here to help. Stay safe always.