Here are the possible causes unpaid bills won't show up on the Pay Bills Online page in QuickBooks Online (QBO):
The unpaid bill isn't included in the filtered transactions.
Other account administrators (Master or Company) paid the bill.
When you're unable to see an unpaid bill listed on the Pay Bills Online page, you need to make sure you've filtered the correct date from the Filter option. This way, you're able to view the complete list of your unpaid bills and start managing them accordingly. Here's how:
Go to the + New button.
Select Pay bills online.
Click the Filter option.
Choose the necessary information (i.e. Due Date, Payee, Division).
I've attached a screenshot below that shows the last three steps.
Then, you'll also need to check with other account administrators if they're able to pay the bill you wanted to pay. When none of them confirms, I'd recommend pulling up the Unpaid Bills, Bill Payment List, and Bills and Applied Payments reports to check. This way, you're able to verify the real status (paid or unpaid) of the bill. Just go to the What you owe section from the Reports menu's Standard tab.
Additionally, here's an article that answers the most frequently asked questions about Online Bill Pay: What is Online Bill Pay?. It includes topics about features, benefits, software compatibility, and troubleshooting procedures to name a few.
Please know that you're always welcome to comment below if you have other concerns or follow-up inquiries about monitoring unpaid bills and other expense transactions in QBO. I'm just around to help. Take care.