Alexa Proactive Events API returns 403 for unicast type -- No enablement for clientId - alexa

Question

I am using Amazon's Alexa skills API and proactive events API to send notifications to my Alexa skill. I am able to send notification with multicast, but it does not work for delivery type "Unicast"
I am getting HTTP status code: 403 and error message as:
"No enablement for clientId:amzn-*********"
I have followed the Alexa skills proactive API documentation
When sending notification to endpoint
https://api.amazonalexa.com/v1/proactiveEvents/stages/development
I obtain the accesstoken using skill credentials and add the accesstoken as bearer token to the request.
Note: I have already enabled the skill from https://alexa.amazon.in and
I got the Amazon userId, apiAccesstoken, and consentToken. I stored them in my database (mongoDB).
I use the Amazon userId to send the notification
<pre>
<code>
var uuid = require('node-uuid');
var accessToken = "This`enter code here` token will be obtained from amazon oauth api.";
var userId = "amzn1.ask.account.AH2ZEP5WGJGAEPWPOG3Getc.....";
var uuid = require('node-uuid');
var referenceId = uuid.v4();
var now = new Date();
var expiresOn = addMinutes(now, 300);
var eventData = {
"timestamp": new Date(),
"referenceId": uuid,
"expiryTime": expiresOn,
"event": {
"name": "AMAZON.MessageAlert.Activated",
"payload": {
"state": {
"status": "UNREAD",
"freshness": "NEW"
},
"messageGroup": {
"creator": {
"name": "Andy"
},
"count": 5,
"urgency": "URGENT"
}
}
},
"localizedAttributes": [
{
"locale": "en-US",
"MessageAlert": "UNREAD"
},
{
"locale": "en-GB",
"MessageAlert": "UNREAD"
}
],
"relevantAudience": {
"type": "Unicast",
"payload": {
"user": userId
}
}
};
var opt = {
data: eventData,
token: accessToken
}
sendRequest(opt, function(err, ret, code) {
console.log("err : ",JSON.stringify(err, null, 2));
console.log("ret : ",JSON.stringify(ret, null, 2));
console.log("code : ",JSON.stringify(code, null, 2));
});
function sendRequest(options, callback) {
var data = options.data;
var token = options.token;
var headers = {
"Content-Type": "application/json",
"Authorization":"Bearer "+token
};
var opt = {
url: "https://api.amazonalexa.com/v1/proactiveEvents/stages/development",
method: "POST",
headers: headers,
body: JSON.stringify(data)
};
request(opt, function(error, response, body){
var statusCode = (response && response.statusCode) ? response.statusCode : "";
if(error) {
return callback(error);
} else if(body) {
try {
var result = JSON.parse(body);
return callback(null, result, statusCode);
} catch(e) {
console.log("e.message : ",e.message);
return callback(null, body, statusCode);
}
} else {
return callback(null, body, statusCode);
}
});
}
</code>
</pre>
The result should be HTTP status code with 202.
But I receive the HTTP status code 403 and the error message as:
"No enablement for clientId: *************"