Set group generates Request failed

Summary

Setting a group in the participants overview generates "Request failed, Unsupported media type "application/x-www-form-urlencoded" in request."

Steps to reproduce

Set group

Example Project

https://grady.informatik.uni-goettingen.de/gdpi-exam/wise2022/

What is the current bug behavior?

What is the expected correct behavior?

Relevant logs and/or screenshots

Possible fixes