Please help,
I've been trying to create a function to generate Access token. It's working when there is no limit on Developer Key as I get Access Token in the response.

When I send a request to get the access token via "/login/oauth2/token", the response has Access Token as NULL. I have the bellow params submitted as JSON

"client_id=id"
"client_secret=key"
"code=abcdefg..."
"grant_type=authorization_code" **** tried with and without this and still get NULL access token

Response from Canvas
"{""access_token"":null,""token_type"":""Bearer"",""user"":{""id"":1,""name"":""My Account",""global_id"":""123456789"",""effective_locale"":""en""},""canvas_region"":""us-east-1"",""expires_in"":-664}"

What am I missing here? 
Let me know.
Thanks.