I know it has to have 2 hearts but I already leveled up an eevee with 2 hearts on Pokemon amie and nothing happened.
to evolve an eevee into a sylveon you must
A) have an eevee with 2 hearts in Pokemon amie
B) have that same eevee know at least 1 fairy type move
then level it up in any way and it will evolve into a sylveon
Hope I helped
You must teach it a Fairy Type Move.
Doesn't matter which, just a Fairy Type move. There are a few TMs that are Fairy Type. By now, you should have one of those. You can use one on Eevee then level it up.
Hope I helped!