Making access_token request using signed JWT

Question

Below is how I am generating the signed JWT .I have created a service account in Google cloud platform console and using its credentials.

const sig = jwt.sign({
   "iss":"[email protected]",
   "scope":"https://www.googleapis.com/auth/business.manage",
   "aud":"https://oauth2.googleapis.com/token",
   "iat":Math.floor(Date.now() / 1000),
   "exp":Math.floor(Date.now() / 1000) + (60 * 60)
  },
  key.private_key,
  {algorithm: 'RS256'}
);

I am making a post request using the JWT to request access_token this way

var data = querystring.stringify({
  grant_type : 'urn:ietf:params:oauth:grant-type:jwt-bearer',
  assertion : sig
});

const options = {
  url : 'https://oauth2.googleapis.com/token',
  headers : {
     'Content-Type': 'application/x-www-form-urlencoded' 
  },   
 form : data
};

request.post(options, function(error,response,body){
  if(error){
    console.log("Post Error : ",error);
  }
  console.log("Body : ",body);
});

I can see the access_token generated OUTPUT OF body :

Body :  { 
    access_token:
    'ya29.c.Kp0B6AfFvBqcKU6Jpo_AX7BiwO0ihmjNltLGDvIJl-Lt1K6rZ8VMhrego635lK3er-BDPmnvIoGJMkbpQaNRLRhDsslWvyLt_zDmMeNCPxUsdH1E2-Vn--myztfTq5uZlhsQfxEWSszy0n5tMlnnB56odxH-mcrlrvi2pxFp4soOB6K-aVdM_yWnO_iyor9WLc0Mme6szRgFmd2qTATMeA',
    expires_in: 3599,
    token_type: 'Bearer' 
}

But whenever I use this access_token to access Google My Business API. It gives the error

{ error:
   { 
      code: 404,
      message: 'Requested entity was not found.',
      status: 'NOT_FOUND'
   }
}

Can anyone please help me out to figure out where am I going wrong ? Thanks.