Set Zahlungsziel_mit_Skonto type as Dateand Time and check or you can convert [%CurrentDateTime%] into String
Well, I have had a look in Studio. It has been a while since I have been here, but not a lot has changed in a year or so. The [%CurrentDateTime%] is not yet available in a Decision in Mendix Studio. All the DateTime tokens are not yet implemented here. Studio has only limited functionality at this time and is only useful for minor tinkering. You best switch to using Desktop version, Studio Pro, which has far more possibiilities