I am unable to generate access token even after following this guide. I get the below response:
The error "unsupported_grant_type" is displayed when the grant_type parameter is not specified, or the given value is incorrect. Note that more often than not, this happens when the parameter is part of the URL. See below example, this is incorrect:
Note: Parameters should be passed in the body of the request, not in the URL.
For reference: Below are the screenshots of a setup using postman tool: