Fund loss in passThruGate() of FixedPricePassThruGate becasue only some portion of user payed amount has been used and the rest of it don't returned to user

Lines of code Vulnerability details Impact If user pay extra ether for minting NFT, then those extra ethers will be locked in FixedPricePassThruGate forever. because passThruGate of FixedPricePassThruGate transfer only NFT cost to gate.beneficiary and don't return extra amount in msg.value to buy...