API not working... postman could not get any response

Hi guys, I am getting something from mysite API as such:(lets say my sites name is mysite)
mysite.com/vanilla/api/discussions
is showing some JSOn and is working. But i can't get postman to work for my api! It's really annoying
It says it could not get any response.
I used this tutorial to do the steps:
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Comments
You might want to post the details of your Postman request here to see if anyone can spot a problem there, rather than assuming it's the API addon.