Hi there, @davwinter-hotmai.
It's my priority to help you connect your bank account to QuickBooks Online. However, I'd like to know if you received an error message while connecting your account and what bank are you working with. Any additional details are much appreciated.
On the other hand, we've updated our Online Banking platform to Open Banking. It means that bank data can only be downloaded into QuickBooks via Open Banking. PayPal and HSBC already support this functionality. This is a part of a new regulation that allows customers to share their financial information electronically.
For those financial institutions that do not support this feature, are advised to manually import their bank transactions using CSV file uploads until the new connection is made available.
Here's a link that can guide you on how to upload your bank transactions in QBO: Manually upload transactions into QuickBooks Online.
Moreover, I got here a reference which provide a short video clip on how to connect your account using the Open Banking. Feel free to check this out: Connect your bank feed using Open Banking.
If you're still unable to connect your account after following the procedure above, I suggest contacting your financial institution. This is to verify if they have system issues, which can be the reason behind the problem that you've encountered.
You can always leave a reply below if you have any other questions. I'll make sure you're all set. Have a nice day!