Invalid argument supplied for foreach() in web service API - php

Question

I'm using PHP code to call Json API, but I'm having Issues loading.
PHP code
$response[$i]['id']=$dataFriend[$i]['id'];
$response[$i]['name']=$dataFriend[$i]['name'];
$response[$i]['id']=$id;
$response[$i]['lastMSGFrom']=$msg_from;
$response[$i]['lastMSGType']=$type;
$response[$i]['lastMSG']=$msg;
$response[$i]['lastMSGTime']=$time;
$response[$i]['lastSeen']=$dataFriend[$i]['date'];
$response[$i]['status']=$dataFriend[$i]['status'];
}
}
foreach ($response as $key => $row) {
$volume[$key] = $row['lastMSGTime'];
}
array_multisort($volume, SORT_DESC, $response);
array_unshift($response, $userData);
Error log
PHP Warning: Invalid argument supplied for foreach()
PHP Warning: array_multisort(): Argument #1 is expected to be an array or a sort flag
PHP Warning: array_unshift() expects parameter 1 to be array, null given
PHP Warning: Invalid argument supplied for foreach()
PHP Warning: array_multisort(): Argument #1 is expected to be an array or a sort flag
PHP Warning: array_unshift() expects parameter 1 to be array, null given
I would appreciate any ideas?