The aba.file I just created to pay multiple suppliers did not save, however all the bills have been marked as paid. How do i undo old aba.file so i can create a new one?

Hi customcafe-acc-g,

As you have previously recorded the bills as paid once downloading the ABA file, you need to undo these Bill Payments so you can create a new valid ABA file.

1. Go to the Expenses menu, then filter to Bill Payments and any relevant date range/payee as required.
2. Select the bill payments and under the Batch Actions tab, select Reverse bill payments.
3. Go to the +New button, select Pay bills and recreate your batch payment and download the new ABA file.

For more insights on how ABA files work in QuickBooks Online, I suggest reading up on this article here

Jess.