The cause:

If you're trying to export from Pleo to Exact, but you don't have bookkeeper-level access in ExactOnline, then the export will fail.

The solution:

Please make sure that you are logged in to Exact Online with bookkeeper access, and then re-try the export from Pleo. If you can't see the "bookkeeper" access option under your Exact account details, please check with your bookkeeper (as they will likely have this permission level).