If you see such an error during export to Mautic, the problem can be due to the invalid authorization details or your account may have been cached.
So, first of all, I would recommend to check the correctness of your authorization details.
Please be advised that for successful export the "API enabled?" and "Enable HTTP basic auth?" controls should be activated in your Mautic account. You can find these controls in your "Configuration" → "API Settings" menu.
If you sure that authorization details absolutely correct, then clean the cache of your Mautic account.
There are several ways to do that. The easiest is to go to the /app/cache folder and delete its content. If you want to do it via CLI command, navigate to the Mautic root folder and run rm -rf app/cache/*. The new cache files will generate itself after the next Mautic refresh in the browser.
To find more detailed instructions on clearing the cache, please follow this link - https://docs.mautic.org/en/troubleshooting#:~:text=Clear%20the%20cache&text=The%20easiest%20is%20to%20go,Mautic%20refresh%20in%20the%20browser
If you still won't be able to export the email, please contact us in chats or write to us at firstname.lastname@example.org.