I am trying to generate Access Token using the URL: https://accounts.zoho.in/oauth/v2/token

and sending    {"client_id"}

                 {"client_secret"}

                 {"refresh_token"}

                 {"grant_type"="refresh_token"} in parameters

in the response I am getting {"error":"access_denied"} ans sometimes {"error":"invalid_code"}

Even if I am trying to generate the access token for the first time I am getting these errors for different zoho crm accounts.

Please suggest if I am doing anything or any step wrong. Please guide me.