Google reader api mark an item as Unread

With the first one url I can mark a post as read but the second one doesn't work. Is this the correct request to mark an item as unread?

//THIS ONE WORKS AND I CAN MARK MY ITEM AS READ
NSString *url=[NSString stringWithFormat:@"https://www.google.com/reader/api/0/edit-tag?a=user/-/state/com.google/read&i=%@&T=%@", entry.identifier, token];

//THIS ONE DOESN'T WORKS AND I CAN'T MARK开发者_JS百科 MY ITEM AS UN-READ
NSString *url=[NSString stringWithFormat:@"https://www.google.com/reader/api/0/edit-tag?a=user/-/state/com.google/kept-unread&i=%@&T=%@", entry.identifier, token];

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In addition to adding the kept-unread tag, you also need to remove the read one (with the r parameter). The request would look like:

NSString *url=[NSString stringWithFormat:@"https://www.google.com/reader/api/0/edit-tag?a=user/-/state/com.google/kept-unread&r=user/-/state/com.google/read&i=%@&T=%@", entry.identifier, token];