Why can't I use vitamins on Camerupt in S/V?

Question

I have tried to use the proteins and HP up and the other ones on camerupt and it comes up saying it won't have any effect on it,

Comments

That message will usually come up if your Pokémon already have max EV’s. That means it already has 510 EV’s.

Answer 1

Your Pokémon already has max EVs.

In all core series games since Generation III, vitamins that affect stats increase a Pokémon's EVs for a given stat by 10 EV points, but can't increase the total EVs beyond a maximum of 510.

Since your Pokémon already has 510 EV points, it can't get any more EVs, unless if you decrease the EVs using an EV-reducing Berry, and then increase the EVs with the stat you choose.

Source (Vitamins)