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Why I don't have to pay gas for listing an NFT on opensea?

How can this be done, is it a signed voucher? Any sample code that I can take a look?

Solution

  • Until anyone buys the NFT, it does not exist on the blockchain. It's "just" a record in OpenSea's offchain database.

    Only when they buy the NFT through OpenSea, the buyser sends a transaction - effectively paying gas fees to mint the NFT.

    Code example of signing a message and validating with ethers.js

    const message = "hello";
const [signer] = await ethers.getSigners();
const signature = await signer.signMessage(message);

console.log(
    ethers.utils.verifyMessage(message, signature) == signer.address
);