Implementation contract receiving struct data and corresponding signature

SignedData2B.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
import './Signed.sol';

contract SignedData2B is IERC721, Signed{
  struct MintParams{
    uint id;
    uint quantity;
    uint32 expires;
  }

  uint public price = 0.01 ether;
  mapping( uint => bool ) public used;

  constructor()
    //the address of our "signer" from step 1
    Signed( 0xd3bDe284cbdE2450EfdDA6f00D335467eB5fCc7b )
  {
  }

  function presale( MintParams calldata params, bytes32 calldata signature ) external payable {
    require( _isAuthorizedSigner( abi.encodePacked(params), signature ),  "account not authorized" );
    require( !used[params.id] );
    require( params.expires > block.timestamp );
    require( params.quantity * price == msg.value );


    used[params.id] = true;
    uint tokenId = totalSupply();
    for( uint i; i < params.quantity; ++i ){
      _mint( msg.sender, tokenId + i );
    }
  }
}