send email using gmail api Error: This API does not support parsing form-encoded input

I'm trying to send email using gmail-api, I'm reading data from user and converted it to base64url string

I'm getting the raw value and when I try to send the mail using post request

 var ss=new Buffer(message).toString('base64')
 var rawdata = ss.replace(/\//g, '_').replace(/\+/g, '-');
 var options={"access_token":google.accessToken,'raw':rawdata};
 var res=HTTP.post('https://www.googleapis.com/gmail/v1/users/me/messages/send',{params: options});

It is throwing error 

    {  "error": {   "errors": [    
    {     "domain": "global",     
           "reason": "parseError",     
          "message": "This API does not support parsing form-encoded input."    }   ],   

   "code": 400,   "message": "This API does not support parsing form-encoded input."  } }

I'm sending following params

var message = 'From: Me <ff@gmail.com>\r\n' +
        'To: Me <ss@gmail.com>\r\n' +
        'Subject: Hello\r\n'+
        'Mime-Version: 1.0\r\n'+
        'Content-Type: text/html; charset=utf-8\r\n' +
        'Content-Transfer-Encoding: quoted-printable\r\n\r\n' +
        '<html><body>' +
        '<h1>World</h1>' +
        '</body></html>';

I'm using valid emails in my app,

Important thing is when I paste the generated raw in gmail-api explorer,

It is working fine and the email is sending, but when I send post request with the same raw it is throwing error.

EDIT: accesstokens are also fine, they are working for other queries.

What is the error in my code?I suppose the error is with headers.

Any help appreciated.

I would suspect that when you don't specify a 'Content-Type'-header, it defaults to "application/x-www-form-urlencoded". Try specifying the Content Type yourself to "application/json".