What to do if you see the message "You have specified the project but no cost type"

The cause:

One or multiple expenses in Pleo are missing a tag. When the projects module is enabled for the Pleo integration, any Pleo expense that has a projects tag also needs a cost type tag (and vice versa).

The solution:

Add the missing tag (project or cost type) to the expense in Pleo and re-try the export.