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.
Thanks for reaching out here. Your banking is a vital part of your business and it's important that you're able to keep your accounts balanced. QuickBooks Online is a dynamic program to ensure you're able to complete your bookkeeping goals with confidence. I'll be happy to assist!
One of the first steps is to clear cache on your browser and then log into your QuickBooks account using a private or incognito browser as mentioned by Fiat Lux. In addition, if there's a break in the connection between your financial institution and QuickBooks, this would cause the unexpected behavior you're currently experiencing. If the issue persist, please contact us so we can take a deeper look into the situation from our end, after gathering additional information.
In the interim, you can manually upload your transactions by following this article. It's important to make note of the last transaction in QuickBooks to prevent duplicate entries, before proceeding through the steps for the manual upload.
Feel free to reach back out if you have any other questions or concerns. We'd love to help!