How to map ID of CaseID from a sucessfull form submit?

Hi, i’m using bonitasoft 7.1.5 and i’m trying to map the Caseid from a successful form Submit to get the id of the next task in the list. In theory it works, when i press submit in the form i can see the caseID that i get from the request, but the variables from wich i get the id remain empty, any idea why?
Example:

  • got 2 variables.