I have all the steps you'll need to fix bank connectivity issues in QuickBooks Online.
Before we start, may I ask the name of your bank to verify and check any open investigation? Any additional info would be much appreciated.
Here are the following scenarios why you're unable to connect your bank account:
The bank may not be a participating bank.
Your bank might not connect to all types of accounts (for example, personal accounts vs. business accounts).
The bank is having system maintenance.
Some banks have multiple names on our list. You might want to check and select the correct one or try all possible bank URLs.
You can reach out to your bank and check for any maintenance update or request to establish a connection with QuickBooks.
Let's also reconnect your account using a private browser to help us determine if this is a browser-related issue. To access QuickBooks using incognito, you may use either of these shortcut keys:
Google Chrome, press CTRL + Shift + N
Mozilla Firefox: press CTRL + Shift + P
Safari: press Command + Shift + N
If you're able to connect your bank account, go back to your regular browser and clear its cache. If you're still getting the same results, you can use other supported browsers instead. It could be that the one you're currently working on has a temporary problem with QuickBooks.