function deposit(bytes32 _listingHash, uint _amount) external {
        Listing storage listing = listings[_listingHash];

        require(listing.owner == msg.sender);

        listing.unstakedDeposit += _amount;
        require(token.transferFrom(msg.sender, this, _amount));

        emit _Deposit(_listingHash, _amount, listing.unstakedDeposit, msg.sender);
    }