https://scarletviolet.pokemon.com/en-us/events/dialga-palkia-raid/#
Catch Version-Exclusive Legendary Pokémon!
You have until Thursday, December 21, 2023, at 3:59 p.m. PST to challenge these Legendary Pokémon in Tera Raid Battles! Dialga is appearing in 5-star Tera Raid Battles in the Pokémon Scarlet game and Palkia is appearing in 5-star Tera Raid Battles in the Pokémon Violet game.
Dialga and Palkia cannot normally be encountered in Paldea, and the Dialga and Palkia appearing during this event both have Dragon as their Tera Type. Try joining Tera Raid Battles hosted by Trainers playing the other version of the game to help complete your Legendary Pokémon collection!
There are a few other active codes atm as well.
https://www.nintendolife.com/guides/pokemon-scarlet-and-violet-mystery-gift-codes-list