It seems like the API-Docs are outdated. Please update (Zephyr Scale Server API (v1) (smartbear.com))
e.g. DELETE existing (of course) TestCase is not working like documented.
Steffen hey wrong community to post in (if you just click on sb community logo, you can navigate into the applicable tool that you are asking the question for), but in your case, it looks like you're hitting the wrong end point.
I see that you're sending the request to [your-jira-instance]/rest/tests/1.0/testcase/{testcaseKey}
I dont know where you got [your-jira-instance]/rest/tests/1.0/testcase/{testcaseKey} the TESTS portion highlighted there, as within the REST api docs that you linked, it shows how to access the individual endpoints (no "tests" anywhere there)
so the short of it is, use the endpoint [your-jira-instance]/rest/1.0/testcase/{testcaseKey} instead.
