code: public function chatAddUser($chat, $peer, $msgToForward = 100)
      {
          $chat = $this->escapePeer($chat); //Not escapeStringArgument as chat needs underscores if spaces in name
          $peer = $this->escapePeer($peer);
  
          return $this->exec('chat_add_user ' . $chat . ' ' . $peer . ' ' . $msgToForward);
      }
docs: Add a $peer to a group chat. Sends him the last $msgToForward messages from this chat
  
  @param        $chat
  @param string $peer
  @param int    $msgToForward
  @return mixed