I've got some steps we can perform to get the Online banking working, jpdunnltd.
May I know what's your bank provider? This way, I can check here on our end if there are any reported cases from other customers or an ongoing investigation.
When there are problems when updating your bank, it's possible your financial institution is doing some updates. It could be also they are having some system maintenance or upgrades. We might want to consider giving them some time to complete their works.
Cases like this, let's try checking on their website to see if there's something that needs approval from you. Then, manually update your bank account again to refresh the connectivity in QuickBooks Online (QBO).
Once done, please reach out to our Customer Support Team. They'll pull up your account in a secure environment and investigate what's causing this bank update issue.