Hi Nick Lynch,
Welcome to the Community. It would be my pleasure to answer any questions you may have with connecting a bank account.
When connecting the business account with QuickBooks Self-Employed, the credentials that you need to use should be the same with your login for the bank's website. If you're still unable to succeed after entering the correct information, I recommend changing your password from your financial institution's website.
Once done, you can repeat the connection process by logging into your Self-Employed account. For the detailed steps, I recommend checking this article about errors connecting a bank:
Errors Connecting a Bank.
Please reach out to me for any additional help you need with connecting a bank. The Community has your back.
