Pokémon GO Gyms have been disabled, will return when the next update rolls out to all players

Pokémon GO Gyms have officially been disabled by developer Niantic. They will return once the next major update rolls out to all players around the world. The Raid Battle feature will then be rolled out slowly over the next few weeks, starting as a beta, with raids visible only to a subset of players at certain Gym locations. Over a few days, Niantic will invite more players to participate and enable raids at more Gyms around the world. Keep an eye on our social media channels for updates on when you’ll be able to start battling in raids.

Source: @PokemonGoApp