Error on creating contact.

[aknamdeo]

I am creating contact using following code.

$newc = new Contact;
$newc->setDisplayName('Ashish10');
$newc->setFamilyName('Namdeo10');
$newc->setGivenName('AKN11');
$newc->setEmailAddress('ak1naxxxxx@gmail.com');
$newc->setGroup(451121);
$newc->setMsisdn('919891xxxxxx');
$rest->save($newc);

But its throwing Internal Server Error on smsglobal script.
[content:protected] => {"error":"Undefined index: group on line 37 in /var/www/api/rest-api/src/Rest/Resource/Field/Validator/Unique.php"}
[handle:protected] => Resource id #2
[headers:protected] => HTTP/1.0 500 Internal Server Error

Is this issue in client script or on smsglobal script.