func: function deposit(bytes32 _listingHash, uint _amount) external {
          Listing storage listingHash = listings[_listingHash];
  
          require(listingHash.owner == msg.sender);
          require(token.transferFrom(msg.sender, this, _amount));
  
          listingHash.unstakedDeposit += _amount;
  
          _Deposit(_listingHash, _amount, listingHash.unstakedDeposit);
      }