Rest API approve request

Hi, im trying to approve a complex workflow through the REST API.

As documented im using this endpoint:

The problem is that my workflow has some input fields that must be completed. I tried send all dataitems in the payload with no effect, no values are arriving to the workflow. I logged in the catalina the flowdata and all i get are empty strings/null values.

The workflow is fine, when used through the ua portal works flawless.

Is there some special way to build the payload? Has someone ever tried this? Other endpoints have fake documentation, is this the case?

Thanks in advance!