Hello there, 2020srp.
I know how you can add a sequential number to your bill payment. I'm here to guide you through the steps.
You'll have to enter the bill payment manually. From there, the system will follow the sequence automatically. Here's a screenshot as your visual guide:
I've also added this article if you want to pay bills with QuickBooks Bill Pay: Enter and manage bills and bill payments in QuickBooks Online.
I'm always around whenever you have concerns about keeping track of your bills and bill payments.