// Creates the user agent
var userAgent = new SIP.UA({
    uri              : '<ext>@<server_url>',
    wsServers        : ['ws://<server_url>:8088/ws'],
    authorizationUser: '<ext>',
    password         : '<ext_password>',
    hackIpInContact  : true
});

// Call options
var options = {
    media: {
        constraints: {
            audio: true,
            video: false
        },
        render: {
            remote: {
                audio: document.getElementById('example-audio-tag'),
            },
        },
    }, 
    extraHeaders : [ #SIP headers for Click2Dial Settings
        'X-Platforma-Outbound-ID:<outbound_id>',
        'X-Platforma-Contact-Ref:<custom_call_ref>'
    ]
};

// Make the call
var session = userAgent.invite('sip:<callee>@<server_url>', options);
 
// Error while placing a call
session.on('failed', function (request) {
    //http://sipjs.com/api/0.7.0/causes/
    console.log('Call Failed');
	//We send back special error messages for validation errors.
	var validationErrors = request.getHeaders('X-Platforma-Error');
 
	if (0 < validationErrors.length) { 
		validationErrors.forEach(function(error) {
			console.log('Validation Error: ', error);
		});
	} 
});