Using dispatch_group to execute code synchronously, this sample singletone class might help to implement it easily.

DispatchGroup.h

#import <Foundation/Foundation.h>

@interface DispatchGroupManager : NSObject
{
}

/**
*  Singleton constructor
*  @return Singleton instance of DispatchGroup.
*/
+(instancetype)sharedManager;

/*
 * Initiate a group of of tasks. Once all tasks are finished, a completion block will execute
 */
-(void)initGroupTasksWithName:(NSString*)groupName;

/**
 *  Supply a completion block once all the async tasks are finished
 *  @param the completion block to execute once all the group tasks are done.
 */
-(void)addGroupTasksCompletion:(void(^)())completion forGroup:(NSString*)groupName;

/**
 * Should be called when a async task in about to be added in taskGroup
 */
-(void)addFollowingTaskToGroup:(NSString*)groupName;

/**
 * Should be called when a async task in done in taskGroup
 */
-(void)doneThisTaskInGroup:(NSString*)groupName;

@end

DispatchGroup.m

#import "DispatchGroupManager.h"

@interface DispatchGroupManager()
@property (strong, readwrite, nonatomic) NSMutableDictionary *asyncTasksGroupDic;
@end

@implementation DispatchGroupManager

#pragma mark - Shared Manager Initialization
+ (instancetype)sharedManager
{
    static dispatch_once_t pred;
    static DispatchGroupManager *DispatchGroupManager = nil;
    dispatch_once(&pred, ^{
        sharedInstance = [[DispatchGroupManager alloc] init];
    });
    return sharedInstance;
}

#pragma mark - Group task methods

-(void)initGroupTasksWithName:(NSString*)groupName
{
    if(!groupName)
        return;
    
    if(!self.asyncTasksGroupDic)
        self.asyncTasksGroupDic = [[NSMutableDictionary alloc] init];
    
    dispatch_group_t oldDispatchGroup = [self.asyncTasksGroupDic objectForKey:groupName];
    if(oldDispatchGroup){
        [self.asyncTasksGroupDic removeObjectForKey:groupName];
    }
    dispatch_group_t dispatchGroup = dispatch_group_create();
    [self.asyncTasksGroupDic setObject:dispatchGroup forKey:groupName];
}

-(void)addGroupTasksCompletion:(void(^)())completion forGroup:(NSString*)groupName
{
    if(!groupName)
        return;
    
    dispatch_group_t dispatchGroup = [self.asyncTasksGroupDic objectForKey:groupName];
    if(dispatchGroup){
        dispatch_group_notify(dispatchGroup,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^ {
            if(completion){
                dispatch_async(dispatch_get_main_queue(), ^{
                    completion();
                });
            }
        });
    }
}

-(void)addFollowingTaskToGroup:(NSString*)groupName
{
    if(!groupName)
        return;
    
    dispatch_group_t dispatchGroup = [self.asyncTasksGroupDic objectForKey:groupName];
    if(dispatchGroup){
        dispatch_group_enter(dispatchGroup);
    }
}

-(void)doneThisTaskInGroup:(NSString*)groupName
{
    if(!groupName)
        return;
    
    dispatch_group_t dispatchGroup = [self.asyncTasksGroupDic objectForKey:groupName];
    if(dispatchGroup){
        dispatch_group_leave(dispatchGroup);
    }
}

@end

MySampleViewController.m

#import "DispatchGroupManager.h"

#define TRAVEL_OVERVIEW_GROUP_TASK  @"localTravelOverviewGroupTask"

@implementation MySampleViewController

//.... Other codes .....
    
//This is a sample method where you need 2 API calls to finish to finally show the result in the tableView
-(void)loadAllTicketsAndHotels
{
    __weak typeof(self) weakSelf = self;
    
    //Initiate the group task
    [[DispatchGroupManager sharedManager] initGroupTasksWithName:TRAVEL_OVERVIEW_GROUP_TASK];
    [self.view addSubview:_loadingView]; // show a loading view while we load everything
    
  //----------- Task 1. get all tickets-------------------
    [[DispatchGroupManager sharedManager] addFollowingTaskToGroup:TRAVEL_OVERVIEW_GROUP_TASK];

#warning We'r pulling only first page, but need to fetch all by adding the limit param, i.e "limit=1000"
    [TicketsService getAllTicketsForIssueId:self.localTravel.issueIdentifier pageNo:1 completion:^(NSArray *tickets, Pagination *paginationInfo, NSError *error) {
        if (!error && weakSelf) {
            __strong typeof(weakSelf) strongSelf = weakSelf;
            [strongSelf.allTicketsArray addObjectsFromArray:tickets];
        }
        NSLog(@"Done loading all tickets");
        [[DispatchGroupManager sharedManager] doneThisTaskInGroup:TRAVEL_OVERVIEW_GROUP_TASK];
        
    }];
  
    //-------------- Task 2. get all hotels ----------------
    [[DispatchGroupManager sharedManager] addFollowingTaskToGroup:TRAVEL_OVERVIEW_GROUP_TASK];
#warning We'r pulling only first page, but need to fetch all by adding the limit param, i.e "limit=1000"
    [HotelService getAllHotelsForIssueId:self.localTravel.issueIdentifier pageNo:1 completion:^(NSArray *hotels, Pagination *paginationInfo, NSError *error) {
        if (!error && weakSelf) {
            __strong typeof(weakSelf) strongSelf = weakSelf;
            [strongSelf.allHotelsArray addObjectsFromArray:hotels];
        }
        NSLog(@"Done loading all Hotels");
        [[DispatchGroupManager sharedManager] doneThisTaskInGroup:TRAVEL_OVERVIEW_GROUP_TASK];
    }];
    
    //---- This method will add the action we want to take once the 2 API calls are finished
    [[DispatchGroupManager sharedManager] addGroupTasksCompletion:^{
        if (weakSelf) {
            __strong typeof(weakSelf) strongSelf = weakSelf;
            [strongSelf.loadingView removeFromSuperview]; //remove the loading view
            [strongSelf generateTravelOverview]; //combine the API call results and show it in the view
        }
    } forGroup:TRAVEL_OVERVIEW_GROUP_TASK];
}


@end