You can only have one financial institution associated with an account in QuickBooks—usually, the financial institution where you hold the account. All the online services that the financial institution offers for QuickBooks will then be available to use with the account.
You can apply for online banking for an account at the financial institution where you hold the account.
If you use online banking and your financial institution offers other online services as well, you can use these additional services with the same QuickBooks account. (You may have to pay additional fees.)
Don't try to use a QuickBooks account at one financial institution with an online service from a different one.
For example, if your financial institution doesn't offer online vendor payment, you can sign up with the QuickBooks Bill Pay Service instead. However, rather than try to use this service with an existing checking account in QuickBooks, create a new QuickBooks account to use with it.