Flickr Search Photo objective-c nothing return

I have a problem with Flickr API. I have created URLString

+ (NSString *)URLForSearchString:(NSString *)searchString {
NSString *APIKey = @"*****";
NSString *search = [searchString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
return [NSString stringWithFormat:@"https://api.flickr.com/services/rest/?method=flickr.photos.search&api_key=%@&tags=%@&per_page=25&format=json&nojsoncallback=1", APIKey, search];}

And then, When I touched search button I called the request with NSURLSession.

- (void)searchFlickrPhotos:(NSString *)text {
NSString *urlString = [FlickrHelper URLForSearchString:@"Nature"];

NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
[request setURL:[NSURL URLWithString: urlString]];
[request setHTTPMethod:@"GET"];
[request setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
[request setValue:[UIDevice currentDevice].name forHTTPHeaderField:@"device"];
[request setTimeoutInterval:15];

NSURLSession *session;
session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];

NSURLSessionDataTask * sessionDataTask = [session dataTaskWithRequest: request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
    NSDictionary *temp = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:&error];
    dispatch_async(dispatch_get_main_queue(), ^{
        //For UI updates in main thread
    });
}];
[sessionDataTask resume];}

I can't get the response from the server. My temp dictionary is always nil... Would you write some detail solution? I would be very grateful for the help!

Solution

In order to solve this, first

Check whether data is nil.
If it's not nil, then use the following LOC to see the output on the console
```
NSString *str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
```
NSLog(@"RESPONSE: %@", str);

Now, you should be able to get another insight on what's actually happening.