Accessing Drupal site from iOS app; successful login, but access denied when attempting to retrieve user data?

I'm completely stuck on this one. I'm using the Drupal iOS SDK to log users into my app, and it works great. However once my user is logged in (authenticated), I use the following method to try and display user data in a label:

- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.

NSMutableDictionary *userData = [NSMutableDictionary new];
[userData setObject:_userName forKey:@"name"];
[DIOSUser
userGet:userData
success:^(AFHTTPRequestOperation *op, id response) { /* Handle successful operation here */ }
failure:^(AFHTTPRequestOperation *op, NSError *err) { /* Handle operation failire here */ }
];

NSLog(@"%@", userData);
}

In response, Drupal throws me an, "Access denied for user Admin" error (even though I have all of the required Drupal permissions in place). To boot, when I log in via my browser as the same user and navigate to the Services endpoint, I'm able to see the data just fine!

Any ideas? Thank you!