Send a graphql request

I want to send a graphql request to a third part application. (datacake de)
I’m trying with the http module with the following settings:

I’m getting an error: {“errors”:[{“message”:“POST body sent invalid JSON.”}]}

I am not sure which action I should chose. (Make a request, Make a Basic Auth request, …)
I tested a bunch of settings with the headers and query strings but I never worked.
I’m following this
The authentification seems to be working. (I removed the Authorization key in the image)