DOMAIN_SEPARATOR = keccak256(
    abi.encode(
        keccak256(
            "EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"
        ),
        keccak256(bytes(name)),
        keccak256(bytes("1")),
        chainId,
        address(this)
    )
);
name = string(abi.encodePacked(_symbol, (" v1")));
