I'm lvl 45 and i claimed my reward in the web. In game, i see the message of reward, but when i click in "receive" I don't get anything. i claimed my reward in the web when the server shilen had lag. The rewards are: Weapon Pack (B-Grade) - 30-Day X 1 and Fresh Milk X 1.
Had the same problem, empty out some slots. Not only this though make sure the first row (or atleast first slot, worked better with first row) is completely empty. With like 55/80 and first row empty i could get it 55/80 didnt work. With the first 2 slots empty i finally got the items after trying for like 30-45minutes.