The Sandbox team announced on Twitter a few hours ago that its LAND are migrating to a new smart contract. As such, users will need to migrate to the new smart contract as OpenSea will only support listing from the new LAND contract.
The Sandbox is a virtual world built on the Ethereum blockchain, where players can build, own, and monetize their gaming experiences. SAND is up by more than 1% so far today and is trading at $3.718 at press time.