Hello, @mechanicalflower.

The check you're trying to update is a bill payment check. You have accidentally deleted the bill associate with it. Let's open your audit trail to check who and when the bill was removed. Then, let's recreate and reapply the bill payment.

Here's how to view your audit trail:

1. Go to the Reports menu.
2. Choose the Accountant and Taxes.
3. Select Audit Trail.
   • You can click the Customize button to filter the audit trail. This way, you can locate the deleted bill easily.

Once completed, let's recreate the bill. Just make sure to enter the same bill date and details.

1. Go to the Vendors menu.
2. Pick Enter Bills.
3. Enter the bill details.
4. Click Save and Close.

Now, let's link the bill payment check to the bill. Here's how:

1. Open the newly created bill.
2. Click the Pay Bill button.
3. From the Pay Bills window, mark the bill you want to pay.
4. Select the Set Credits button.
5. From the Credits tab, choose the credits you want to use to pay the bill.
6. Click Done.
7. Review the Pay Bills details again.
8. Hit Pay Selected Bills.

You can refer to this article for more insights about to clear your vendors' open transactions: A paid bill or invoice shows on report or window of open transactions.

Keep me posted if you have other questions about managing your transactions in QuickBooks. I'm always here to help.