title: How to tag several friends in a photo using Facebook iOS SDK
body: <p>From Facebook Developer document, I find that
  "You can specify which user to tag using two methods: in the URL path as <code>PHOTO_ID/tags/USER_ID</code>, or in a URL parameter as <code>PHOTO_ID/tags?to=USER_ID</code>. To add several tags at once, you can specify a tags property which contains an array of tags like so <code>PHOTO_ID/tags?tags=[{"id":"1234"}, {"id":"12345"}]</code>. Currently, you cannot tag a Page in a photo using this API."</p>
  
  <p>Here is my code.</p>
  
  <pre><code>NSString *photoID = @"267766096670674";    
  
  [self.facebook requestWithGraphPath:[NSString stringWithFormat:@"%@/tags?tags=[{\"id\":\"%@\"},{\"id\":\"%@\"}]?access_token=%@", photoID, @"100001965796318", @"100004119154586", self.facebook.accessToken]
                            andParams:nil 
                        andHttpMethod:@"POST" andDelegate:self];
  </code></pre>
  
  <p>I get the error as following
  "Error message: Error Domain=NSURLErrorDomain Code=-1000 "bad URL" UserInfo=0x3f55a0 {NSUnderlyingError=0x3f5c10 "bad URL", NSLocalizedDescription=bad URL}"</p>
  
  <p>Due to the document, tag one friend is OK. But why can't I tag several friends at once?</p>