Variables parameter not working in Originate

I am using asterisk 15.5 with default ARI python library from github.

While using originate, I am trying to use variables body parameter to send a PJSIP header, but whenever I add into originate stops working and the call is not getting placed.

I am using variables={“header”:“send-this”} as shown in official documentation.

Kindly tell me if i am doing something wrong?