I've got the steps to resolve the error in Online Bill Pay. This could be a browser-related issue. In the long run, the stored cache can affect the performance of QuickBooks Online that can cause unexpected behavior.
To begin, I suggest logging in to your QuickBooks Online account via a private window. This doesn't use the existing cache files, which makes it a good place to determine if there's an issue with the browser.
Here are the keyboard shortcuts:
Safari: Command + Shift + N
Google Chrome: CTRL + Shift + N
Mozilla Firefox or Microsoft Edge: CTRL + Shift + P
Once signed in, open Pay Bills Online. If it works, let's clear the cache of your browser. This helps remove its stored cache so QuickBooks will perform efficiently.
If private browsing doesn't work, I'd recommend using different browsers. They'll provide you the best and most secure experience with QuickBooks. For more details, see this article: System Requirements For QBO.
However, if the same result, I suggest getting in touch with our QuickBooks Online Support. One of our representatives can securely look into your account to figure out the main cause of this.
I also encourage you to review this article to learn more about paying bills online using QuickBooks: Pay Bills.
Additionally, I've added an article that'll guide you to track your payments. This helps you easily pay and manage all your bills in one place: Payment Tracker.
Let us know if you need further assistance in managing your vendor transactions. Doing so helps us to provide an accurate solution for you.