Dear Chris, Dear oTree users,
I'm trying to retrieve data about a session and its participants using the GET session data endpoint in Qualtrics. Qualtrics offers a Web Service, which usually works fine with the oTree REST API. However, in this case the participant_labels seems to be omitted. I.e., when testing the Web Service, I get all participant's data. 
Do you se an obvious mistake?
Your help would be much appreciated!
Thanks in advance and best,
Felix

The participant label must be passed not as a query parameter but rather as part of the request body. It seems that Qualtrics doesn't allow sending request body along with a GET request. That is understandable as a number of tools don't allow this.

Hi Chris,
thank you for your response! 
I now found a workaround for which I do not use the GET request, but Qualtric's Query Strings.
Best,
Felix