hi, i am trying to upload a video to favorite in my account but it shows Invalid request Uri and status code =400

i dont understand how should i format my request

my code

    NSURL *url = [NSURL URLWithString:
                 http://gdata.youtube.com/feeds/api/users/username/favorite];
ASIFormDataRequest *request = [ASIFormDataRequest requestWithURL:url];
[request setPostValue:@"gdata.youtube.com" forKey:@"Host"];
[request setPostValue:@"application/atom+xml" forKey:@"Content-Type"];
[request setPostValue:@"CONTENT_LENGTH" forKey:@"Content-Length"];
[request setPostValue:@"" forKey:@"AuthSubToken"];
[request setPostValue:@"2" forKey:@"GData-Version"];
[request setPostValue:developer_key forKey:@"X-GData-Key"];
[request setPostValue:xml_data forKey:@"API_XML_Request"];

[request setDelegate:self];
[request setDidFailSelector:@selector(requestFailed:)];
[request setDidFinishSelector:@selector(gotTheResponse:)];
[[networkQueue go];

i have auth token and developer key, VIDEO_ID.but m not sure how to pass xml data in post request:

<?xml version="1.0" encoding="UTF-8"?>
 <entry xmlns="http://www.w3.org/2005/Atom">
  <id>VIDEO_ID</id>
 </entry>

NSString *xml_data = contains xml data in string form