The dossier is required.
Translation: Het dossier is verplicht.
This error message comes from Boekhoudgemak or Multivers Online and indicates that it is mandatory to choose a cost center and a dossier.
You can solve this in Boekhoudgemak or Multivers by following these settings:
Maintenance > Chart of accounts > General tab
Select the relevant general ledger account
Click on the Specialization tab
Select 'Integration' and check the box next to it.