How come I didn't get the level 8 trophy even though I am at level 8 on moshi monsters?

Sometimes, if your monster's health/happiness isn't high enough you won't be able to move up a level. To make your monsters health go up you feed it food from the Gros-sery Store and Green and Roarberry Cheesecake make it go up big time. To make your happiness go up tickle your monster and do lots of puzzles.