    // check to ensure that for ETH orders, enough ETH is sent
    // for non ETH orders, IERC20 safeTransferFrom will throw error if insufficient amount is sent
    if (isMakerSeller && currency == address(0)) {
      require(msg.value >= totalPrice, 'invalid total price');
    }
    // check to ensure that for ETH orders, enough ETH is sent
    // for non ETH orders, IERC20 safeTransferFrom will throw error if insufficient amount is sent
    if (isMakerSeller && currency == address(0)) {
      require(msg.value >= totalPrice, 'invalid total price');
    }
    // check to ensure that for ETH orders, enough ETH is sent
    // for non ETH orders, IERC20 safeTransferFrom will throw error if insufficient amount is sent
    if (isMakerSeller && currency == address(0)) {
      require(msg.value >= totalPrice, 'invalid total price');
    } else {
      require(msg.value == 0, 'non-zero ETH value');
    }
