Let me help you sort this out, Kennedy442.
You encounter the message if you're unable to enter any amount PAYMENT field or you’ve entered a “0.00” amount. In QuickBooks Online, you'll have to enter an amount in the field that should be greater than 0, otherwise, it’s not a payment.
To resolve this, you have two options:
In your case, you can choose the first option since the credit memo is the exact amount of the open invoice.
Feel free to get back to this thread if you have additional questions. We're just one comment away. Take care!
