I can help you in resolving the error you're having with applying a credit memo to an invoice.
It's possible that piled-up cache in your regular browser caused this unusual behavior when trying to apply this credit memo. You can clear your current browser’s cache to resolve this.
You can clear your browser’s cache and cookies to fix them. But first, try using a private browser or an incognito window when trying to apply this credit memo. If you no longer have the error, then you can clear the cache in the one that you're currently using if it works.
If it works, here's how to clear cache and cookies to fix issues when using QuickBooks Online. Restart your browser right after.
You can refer to the following article for more information about creating an applying credit note: Create and apply credit notes or delayed credits in QuickBooks Online.
Here’s also an article that tells you more about handling supplier credits and refunds: How do I handle supplier credits and refunds?.
Let me know if you need more help in applying this credit memo by leaving a reply below. Take care and have a great rest of the day!
I can help you figure this out, sc38.
You'll want to check if the invoice isn't linked to a project. This might be the reason why you're unable to apply the credit note. Also, check the Credit note if it's having the same customer as the same with the invoice.
Once verified, try to link the apply the credit note again. For additional reference, check out this article: Create and apply credit notes or delayed credits in QuickBooks Online.
Keep me posted how it goes. I want to make sure this is taken care of.