To check if the browser-related issue (cache and cookies), try signing into your QuickBooks Online (QBO) using a private browser (incognito).
Press Ctrl + Shift + N (Google Chrome).
Ctrl + Shift + P (Firefox).
Control + Option + P (Safari).
Once logged in, try to connect the bank again to double-check. This can be done by going back to the Banking menu. You can also visit this article for the detailed steps on how to do it: Connect your bank feed.
If it's successful, return to your default browser and perform a clear cache to refresh the system. However, if the issue persists, try using other supported browsers.
Please let me know if you have any other issues or concerns, and I'll get back to you as quickly as possible. I'm always here to help. Have an amazing rest of the day!