usertask contract returns empty arrays

I've called '/API/bpm/userTask//contract' and it returned :
"inputs": [],
"constraints": []
but the task has many input fields in the view.
why the response is like that and what does this api must return?

Connector wont execute on REST call

Hello, i'm currently developing a C# client where I need to instance some process via REST API. I have no problem executing any task with contracts, but when any userTask has a connector (specifically a rest connector to another server of mine), this won't execute and its skipped while the task is completed sending me a success response (Code: 204). However, if I perform the tasks on the portal every connector works perfectly.
The method i'm expecting to execute both the task and connector is {API/bpm/userTask/:taskId/execution} sending the correspondent json with the contract.

How i get a userTaskId?

I searched in Javadocs for a userTaskId method , and i dont find any direct method. its a value from 2 or more method calls? How i reach this value?
My objective is create a Tasks Shelf, anyone who take a task, can return it if dont wanna or simple view that task. and for that i needed a release task, the method needs userTaskId. and when take the task, another tasks became invisible until finish or return a task. using Hide Task method