What is the input and out of a form which contains multiple variable of complex type?

\Hello, Guys!
I'm new to Bonita BPM 7.4.1 and I really need your help.
I'm trying to create a process that the user can make orders. I have a task add order. My order is a business data object and contains around 15 fields from different types (int, text, double, boolean). As input on my task Add order I used the button 'Add from data' and I chose my business object Order. I checked also the checkbox 'Multiple' and when I generate the form it creates me a form with container full with my fields and at the bottom I have two buttons 'Add' and 'Remove', so the users can make couple of orders in one screen. In this form I have generated two variables one is formInput, which is JSON - something like this:
{
"positionInput" : [ ]
}
and one more variable which is formOutput which is Javascript:
return {
'positionInput': $data.formInput.positionInput
};
The form visualize well the both buttons are working, but when I submit the form it doesn't go to the next task in the process and I guess it doen't save the data, that I entered. Can anybody help me with the input and output of the form?
Thank you in advance!
Best regards,
Albena Mincheva.