How do I get my account number with a vendor to appear on a payment processed through QB bill payments?

You’ll need to add your account number as a Custom field in the vendor’s profile to make sure it appears on future checks issued to them, RProto.

Follow these easy steps to complete the task:

1. Open the Vendor Details from the Expenses & Bills menu.
2. Click Edit to update their profile. 
3. Go to the Custom fields section to add one (if you haven't already) by selecting the + Add custom field option.
4. Enter your account number in the Custom field box.
5. Hit Save. 

Also, enhance your QuickBooks experience by partnering with our QuickBooks Live Expert Assisted team. With their expertise, you can simplify processes, boost productivity, and receive personalized guidance tailored to your business’s specific requirements.

We’ll be right here to assist you further if you need additional help with your vendor transactions in QuickBooks.

@RProto 

Another option, you should check Melio to sync with QBO. You will speed up your payment process with their verified network of billers. You just pick your biller and pay. It’s simple and they don’t even need to sign up. Another perk, you can get cashbacks.

https://quickbooks.intuit.com/learn-support/global/manage-suppliers-and-expenses/pay-bills-online/01/1351046