Making a new mega evolution

[Charinjago]

Hello, I'm trying to make a new mega evolution for my Eternal Florges (it's defined as a separate Pokémon, not as a form of Florges, I think this makes it easier to define a mega evolution for it) but it doesn't work. I defined everything (the Pokémon, its mega evo, its mega stone) correctly, it works in game, the only thing is that I can't trigger the mega evolution. For sure the problem isn't with the mega stone, when I make a Pokémon hold it it displays the mega stone icon, but rather with the form change process, the mega Florges works fine.
Can someone help?