How do I assign check numbers using QuickBooks Bill Pay?

Welcome to the Community forum, Lisa.

Currently, it's not possible to modify and assign check numbers using QuickBooks Bill Pay. Once the check has been mailed to the vendor, you can see the check number on the Bill Pay Payments page and the system will assign it to the check automatically.

As a workaround, you can look for a third-party application that can suffice this function.

If you have questions about QuickBooks Bill Pay on how it schedules payments to your vendors, you can read this article: Learn about QuickBooks Bill Pay for QuickBooks Online.

Click the Reply button below if you have additional questions about managing your QuickBooks Bill Pay account. We'll be willing to help. Keep safe, and have a good day.

This is just another way QuickBooks Desktop is better. With Desktop you can assign whatever numbers you want to bill payments, and to most all other transactions as well.

That Online cares and limits you shows how lost the Dev team is: They spend time doing stupid things like this instead of developing features customers want.