Unsupported grant type error in RingCentral
<p>I am calling the API to refresh my access token on RingCentral but it throws the following error </p>

<pre><code>{
    "error":"invalid_request",
    "error_description":"Unsupported grant type",
    "errors":[
        {
            "errorCode":"OAU-250",
            "message":"Unsupported grant type"
        }
    ]
}
</code></pre>

<p>Can anyone help me out?</p>