I appreciate the details you've included in your post, Alethea.

Let me go into details about this and provide some help.

If you're using pay bill when applying for the credit, it will automatically apply for the same amount.

With this, we can perform some troubleshooting steps to fix them as there might be a cache issue that's why your end isn't working.

There are also times when the browser is full of frequently accessed page resources which causes some errors or unusual responses. 

Let's try logging in to your QBO account using a private browser as it ignores websites from using cookies and doesn’t record any history and data. 

You can use either of these shortcut keys on your keyboard to access incognito mode:

• Safari: Control + Option + P
• Google Chrome: Press Ctrl + Shift + N
• Firefox or Internet Explorer: Ctrl + Shift + P

Once this works, it means you have to clear the browser's cache so the system can start fresh. If you get the same result, I recommend switching to a different supported browser as an alternative.

Furthermore, you can browse through this article that I'm adding for you to be able to track bills and record the payments: Enter bills and record bill payments in QuickBooks Online. 

Let me know if you have other concerns about paying bills in QBO. You can drop a comment below, and I'd gladly help. Stay safe, and I wish you continued success.