Can I generate a credit note from an existing invoice, as was possible in QB Desktop?

Welcome back to the community, Egbert. QuickBooks Online doesn't currently have a built-in feature to directly generate an invoice into a credit note.

I suggest submitting your feedback directly to our product engineers so they can consider this for future updates. You can do this by going to the Gear icon > Feedback. Enter your request, then click Next to submit.

In the meantime, you can manually link the Invoice and Credit Memo by creating a Receive Payment. Just ensure that the Automatically apply credits toggle is turned off within your Account and Settings first.

Keeping that setting on allows the software to auto-apply credits to the oldest invoice. Turning it off gives you manual control to choose exactly which invoice the credit covers.

After turning it off, follow these steps:

1. Head over to +Create, then Receive Payment.
2. Choose the customer from the Customer dropdown menu.
3. Under Outstanding Transactions, check the box for the invoice you want to pay.
4. In the Credits section, select the credit note you wish to apply.
5. When you’re done, select Save and close.

You can refer to this article for step-by-step instructions on applying credit notes within QuickBooks Online: Create, apply, or import credit notes and delayed credits in QuickBooks.

If you need further assistance, just click the Reply button.