You detach a fee to fix a billing mistake, run a new bill run, and the new invoice comes out right. But the original fee now shows as "Not Paid," or looks like it's waiting to be invoiced again, even though nothing is actually still owed. Detaching breaks the link between a fee and its invoice on purpose, so the fee can be reinvoiced, and that broken link is exactly what causes the leftover "Not Paid" status. Once you know that, both the fix and the cleanup take a few minutes.

Detaching applies to one-off fees and membership fees on invoices generated through a manual bill run or an automatic one.

If a bill run went out with the wrong due date, wrong revenue account, or another setting mistake, detaching gets the affected fees back into a billable state without touching anything else on the invoice.

The detach in step 1 above is also what causes the symptom you'll likely notice next.

Detaching removes the connection between a fee and its invoice, which makes the fee:

Both are correct, expected side effects of detaching, not a new error. They show up because the fee's only record of being billed was the connection you just removed, not because the fee actually reverted to unpaid in your accounting.

Fees can't be reattached to their original invoice once detached, so which fix you use depends on whether they were actually paid.

If the fee was never paid, invoice it again along with any other one-off fees and membership fees. Then create a credit note for the amount owed on the original invoice, and allocate that credit note to the new one. This keeps your accounting accurate without double-charging the customer.

If the fee was already paid, you don't need to reinvoice it. Click the cogwheel icon next to the one-off fee and select Mark as Paid. Only do this once you've confirmed the payment actually went through, since the system doesn't check that for you.