"Get three Vault tickets with promo code “SQUIG”."

Redeem it in-game or in the account management website to enter The Vault for the first time:
https://account.warpforge40k.com/

The Vault is an additional reward system full of awesome expansion items, from booster packs, to cards and exclusive cosmetics! Check out how it works in the announcement web post:
Learn more about The Vault.