src/whatsprot.class.php
public function sendPresenceSubscription($to)
    {
        $node = new ProtocolNode('presence', ['type' => 'subscribe', 'to' => $this->getJID($to)], null, '');
        $this->sendNode($node);
    }
public function sendPresenceSubscription($to)
    {
        $node = new ProtocolNode('presence', ['type' => 'subscribe', 'to' => $this->getJID($to)], null, '');
        $this->sendNode($node);
    }
public function sendPresenceSubscription ( $ to ) { $ node = new ProtocolNode ( 'presence' , [ 'type' => 'subscribe' , 'to' => $ this -> getJID ( $ to ) ] , null , '' ) ; $ this -> sendNode ( $ node ) ; }
Send presence subscription, automatically receive presence updates as long as the socket is open.

@param string $to Phone number.
Send presence subscription automatically receive presence updates as long as the socket is open .