Calling Rest API, sending a JSON in the request

Hi there, I have been trying to call rest services, sending JSON in the request because my targetted endpoint only accepts a JSON. A text or XML or any other type will not be allowed.  I set up my rest call as follows: After selecting JSON type, it still sends as application/octet-stream and i cannot get the intended request I want.  I can confirm that my end point works, because i tried it in POSTMAN, sending over a json type body. This is the call that i’m trying to achieve, in mendix, in postman.   Is there a workaround for this? Thank you!  
1 answers

Solution was provided by Ronald Catersels.

It was to set appropriate headers in order for the contents to be sent as json! 

This did the trick for me. My end point is returning as intended now.