Bonitasoft returns 0.00 in Database for assigned variables

I created 3 variables which i used to do calculations

i called one numberOfNights = Name , Value = numberOfNights type = String, the second one perdiem = Name , Value = perdiem type = String and the last one
is a javascript expression i used for some calculations

Now i used some Javascript function like this :

var CalculateAmount = Number($data.perdiem) * Number($data.numberOfNights);
return CalculateAmount

when i created another variable of Type Javascript Expression with name PerdiemCalculateDays , now i save.

How to send via formOutput the automatically set date(today)

Hey guys,
I'm new to bonity and have trouble with a date picker. I have a form with a date picker, which is set to read-only because I want to just set the date automatically.

So at this time my value of the date picker is set to "formInput.bvar_ManuskriptEinsendenInput.eingereichtAm", which is of course wrong, because I dont want the client to choose the date. "eingereichtAm" is my date-variable:

business variables do not retrieve the values from the formOutput

I use several business variables to store values chosen by user interaction from UI forms.
After each task I want to use a business variable to store the user selection for a certain type and at the end of the process the last form is supposed to display the selected data from each tasks.