There are certain moves or abilities that prevent sleep, most of which are covered here, but most likely it is because Carbink used the move Safeguard, a move it learns by level up (and by tm)
Safeguard is a move that protects the user's team from status for five turns. As such, no Pokemon on Carbink's team, Carbink included, can be forcibly put to sleep during those five turns, and as such, Hypnosis failed.
There is another possibility that this was on Pokemon Online or Pokemon Showdown, where Sleep Clause was in affect and you already had one sleeping Pokemon, and as such hypnosis failed to put Carbink to sleep
Hope this helps