Good job on successfully importing your transactions last week! The Bank Upload feature in QuickBooks Online helps you bring over multiple transactions at once. There are a couple of reasons why an OFX or QFX format can be invalid. I'll show you how to handle this in your account.
To make sure your current file is compatible with the system, I recommend following the steps in this article: Fix bank upload errors in QuickBooks Online
I also encourage you to clear your cache to ensure there are no bugs in the software due to a browser issue. Here's how to do that: Clear cache and cookies to fix issues when using QuickBooks Online
In case the issue persists, please reach out to our tech support team for us to investigate this further. Here's how to get in touch.
Schedule a Callback: click (?)Help in the upper right > click Contact Us > explain your situation > click Let's Talk > choose Get a callback (Note: Callback hours are the same as regular phone hours.)
I hope this helps! Have a great day.