Let me help provide you with troubleshooting steps for adding your bank account to QuickBooks Online (QBO).
First, consider logging in to your bank website and check for alerts and notifications. If you want to connect your bank account, ensure to copy and paste the updated URL of your bank.
Also, you can use an incognito or private browser during the process of connecting your bank. To do so, press this shortcut key on your keyboard:
Google Chrome: Ctrl + Shift + N
Mozilla Firefox: Ctrl + Shift + P
Safari: Command + Option + P
If the issue persists, please provide the exact error message if there's any.