It's great to see a new face here in the Community. Allow me to gather some additional information so that you're able to fix this error that you're receiving when exporting from QuickBooks Desktop (QBDT) to Online (QBO).
To properly assist you with this issue, are you exporting from DT to QBO locally or on another computer? If so, then please provide me with some more details or screenshots on this matter. If not, then I recommend exporting locally.
In the meantime, you can check out some of the links below that can be helpful for you and your business.
Once I have the other information, I'll be able to give you the answer to your question. I want to make sure that you're able to get back on track. The Community is always here to have your back. I'll be waiting for your response.