Can’t hear the hammer on

Hi everyone. I was learning a song today which involved a hammer on. Usually it works just fine. But it was the middle string and it did not work. I dont know if its because they’re plastic. Any advice?

Hi everyone. I was learning a song today which involved a hammer on. Usually it works just fine. But it was the middle string and it did not work. I dont know if its because they’re plastic. Any advice?