It's important that all your transactions are correctly entered so your account balances can reflect reality. QuickBooks Online is a great tool able to connect to various banks in order to import transactions to save you time with data entry. I can point you in the right direction for assistance.
In order to get this error resolved, I recommend reaching out to the QuickBooks Online support team outside of the community. They'll be able to verify your account info with you as well as the error you see in a secure setting in order to provide some troubleshooting steps as well as check in with our engineers. You can reach out to them using these methods:
Schedule a Callback or start a Chat: click (?)Help in the upper right > type and enter "Contact support" into the QB Assistant > click Contact Us > explain your situation > click Let's Talk > choose Get a callback or Start a Chat. Social Media: Facebook and Twitter
If you have any other questions, feel free to reach out here.
Utilize the trial version of MT Online to isolate the issue. It is designed to import into any bank or credit card in QuickBooks Online, so there is no specific setting needed. If the same error persists, there is an ongoing problem at your bank or connection.