Hello there, @mtalbot5.
This error message occurs when you try to connect a parent account and its subaccounts. In QuickBooks Online, we can only connect either the parent or the sub-accounts.
If all transactions are coming from the parent account, we'll want to connect it instead. If they are downloaded to the sub-accounts, we can select all applicable sub-accounts. We can look into this article for more information about this error message in the Connect the accounts to Online Banking section: About bank or credit card subaccount setup.
You can check out this article for more details: How to add and connect bank and credit card accounts.
I've got a link here that provides you with articles about managing your bank feeds transactions: Banking.
Don't hesitate to drop a comment below if you have other questions. I'm always happy to help. Take care!