Xmpp IOS multiuser chat . i didnot find a way to accept the invitation from group ? how i can accept the incomming invitation

When I send an invitation this function is called, but I can't understand what line of code I should use for accept invitation.

I am trying to create a multi user and multi groups invitation also called did received message function.

- (void)xmppMUC:(XMPPMUC *) sender roomJID:(XMPPJID *) roomJID didReceiveInvitation:(XMPPMessage *)message 
{ 
}

to accept the incoming invitation :

- (void)xmppMUC:(XMPPMUC *)sender roomJID:(XMPPJID *) roomJID didReceiveInvitation:(XMPPMessage *)message
{ XMPPRoom *mu = [[XMPPRoom alloc] initWithRoomStorage:xmpproomMstorage jid:roomJID
                                           dispatchQueue:dispatch_get_main_queue()];

    [mu   activate:xmppStream];
    [mu   addDelegate:self delegateQueue:dispatch_get_main_queue()];

    self.toSomeOne = roomJID;

    [mu activate: self.xmppStream];
    [mu fetchConfigurationForm];
    [mu addDelegate:self delegateQueue:dispatch_get_main_queue()];
    [mu joinRoomUsingNickname:xmppStream.YourJid.user history:nil password:@"Your Password"];
self.toSomeOne = roomJID;
    XMPPPresence *presence = [XMPPPresence presence];
   [[self xmppStream] sendElement:presence];
    [xmppRoster addUser:roomJID  withNickname:roomJID.full];
    [self goOnline];
}