The cause:
One or more Pleo expenses have a tag that reflect a closed project in Fortnox.
There are two alternative solutions:
Change the tag on the Pleo expense(s).
Or
In Fortnox, change project status from “closed” to “ongoing”:
Click Register.
Click projects (Projekt).
Click on the affected project.
Change either the end date or the status of the project:
Click save (Spara).