Hallo @mirco.koenig, your request body seems to have a lot of HTML and other control characters, which might be seen as invalid JSON. The problem is that this fails so early while parsing the request that it’s hard to see what the actual cause is. Can you send a simple text in the task name and description to confirm?
When I did a test just now the task was created without any issues, even with an almost identical task name. Only the description was different. But it still had most of the HTML Elements of the previous Request, since I take a taskbundle and replace placeholders inside the description with new texts.