submit button and access to the next form

I have two human tasks: Step1 and Step2. I want that when I finished the first redirected to the form of the second. In the form of the first task I have defined the following variables:

myTask (externalAPI): ../API/bpm/task/{{taskId}}
myCase (javaScript): return $data.myTask.caseId
urlNextTask (javaScript): return '/form/processInstance/' + $data.myCase +'/task/Step2'

In the "Target URL on success" of de button submit write: /bonita/portal/{{urlNextTask}}

On click, the url to send is literally /bonita/portal/{{urlNextTask}} instead of /bonita/portal/form/processInstance/123/task/Step2 (where 123 is the number of Case)

What am I doing wrong? What I want is to go from one form to the next without going through the portal.