The Pokémon Global Link (PGL) is currently unavailable due to maintenance, which is scheduled to last until 11 p.m. EST – so hopefully it shouldn’t be for much longer. During maintenance, all services on the PGL are unavailable, including the official website, features related to Pokémon Sun and Moon, Game Sync and Rating Battles. If you see the maintenance notice on the PGL at a time other than during the maintenance period described, this means that the site is undergoing emergency maintenance. Pokémon Sun and Moon are also undergoing maintenance.
Source: Pokémon Global Link