The cause:
In e-conomic, the journal that's been created for Pleo has the wrong entry type.
The solution:
Log in to e-conomic.
Go to "Journals".
Select the "Pleo" journal (please check with the person who created the journal if you can't find one called "Pleo").
Click on "Other options".
Click "Journal setup".
Click "Entries".
From the "Allowed entry types" dropdown, select "All".
Click "Save".