Collections

A collection enters a gacha only after Expo has proven that it can buy a token into the vault and deliver it from the vault. Each proof runs on a copy of Ethereum mainnet, through the same path the live contracts use, and the admission is recorded on-chain with a digest of that evidence.

Some collections restrict transfers made by contracts. Expo's vault is a contract, so such a collection can be bought and then not delivered. The proof exists to catch this, and collections that fail it stay out.

A collection's owner can change its transfer rules or upgrade it after admission. Admission binds the code at the collection's address, so new code at that address voids it, and new openings of that gacha are refused until it is admitted again. Changed transfer rules, or an upgrade behind a proxy, do not void it. If such a change blocks delivery, you are compensated at the deadline as described in How an opening works.