Access to form fields in script task

Hi folks,

I’m trying to build a demo for a client and I want to use camunda as some kind of backend wrapper connecting all the loose ends of already existing backend systems. I hope that fits in some way the pupors of camunda?

The main process will process some json objects and pass them around to other systems.
Now, my problem is that I’m not able to get access to the json string of the start event in my first script task. Basically I try to follow this tutorial: https://medium.com/@stephenrussett/deploying-external-scripts-with-camunda-rest-api-e06bd90a2931

But my form field “jsonString” is not accessible as written there:
execution.getVariable(“jsonString”);
Unfortunatly I cannot find anything online or in the documentation.

Regards
Philipp

No ideas? Or am I doing it wrong and should use a java delegate instead?