I just got Hoopa from that Mcdonalds thing but dont know where to get the bottle for Hoopa Unbound?

Question

i tried putting it into my party and walking into the Mauville Pokemon center like you do for Diancie but it didnt work.

Answer 1

>In Pokémon Omega Ruby and Alpha Sapphire, it can be obtained by walking into a Poké Mart with Hoopa in the player's party.

As it says above, just simply walk into a Pokemart with Hoopa in your party, talk to the guy in the corner and he'll tell you a story, when he is done with the story he'll give you the Prison Bottle.

Source

Answer 2

You have to go to the poké-mart there talk to new clerk standing there. of course with hoopa in your party.
source: knowledge.