Note :- Facebook provides only 25 latest chat conversation messages

/This is completion handler method and takes 3-4 sec to load chat messages from FB/

NSMutableArray *arrConversation = [[NSMutableArray alloc]init];

NSArray *arrPermission = @[@"read_mailbox"];
    if ([[FBSession activeSession]isOpen]) {

[FBRequestConnection startWithGraphPath:@"/me?fields=inbox" completionHandler:^(FBRequestConnection *connection,id user, NSError *error) {
    if (error) {
        //Sorry check permission or network.
    } else {

    //Here we can save conversations into an array and print that array...
    arrConversation = [[user valueForKey:@"inbox"] valueForKey:@"data"];
     NSLog(@"%@", arrConversation);
    }
}];
    }else{
        [FBSession openActiveSessionWithReadPermissions:arrPermission
                                           allowLoginUI:YES
                                      completionHandler:^(FBSession *session, FBSessionState status, NSError *error) {
                                          if (error) {
                                              //Sorry check permission or network.
                                          } else {
                                             NSLog(@"%u", status); 
                                          }
                                      }];
        }