我有一个NFT集合的智能合约。关键是我有两种不同的薄荷糖。一个需要灵魂绑定NFT的白名单的造币厂和另一个将是销售集合的造币厂（以MATIC，ETH为成本）。我已经有了灵魂绑定薄荷功能，但我没有得到销售薄荷工作。safeMintNft（）函数被触发以铸造此销售集合。

function safeMintNft() public payable whenNotPaused {
    require(
        nftCost > 0, "NFT cost is not set"
    );

    require(
        keccak256(bytes(whitelistedAddresses[msg.sender].discordUser)) !=
            keccak256(""),
        "Address is not whitelisted"
    );

    require(
        keccak256(bytes(whitelistedAddresses[msg.sender].user_type)) == keccak256(bytes("buyer")),
        "Only buyers can mint the NFT"
    );
    uint256 minterBalance = address(msg.sender).balance;
    require(
        minterBalance >= nftCost,
        "not enough tokens to pay for this NFT"
    );

    
    uint256 tokenId = _tokenIdCounter.current();
    _tokenIdCounter.increment();
    tokenIdAddresses[tokenId] = msg.sender;

    address payable contractAddress = payable(address(this));
    contractAddress.transfer(nftCost);

    _safeMint(msg.sender, tokenId);
}

那我就用茶试试。达到这种情况的代码片段如下：

describe("User has enough eth to mint", async function() {
     beforeEach(async function() {
         await this.nft.setNftCost(ethers.utils.parseEther("0.1"));
      });
      it("should be able to mint", async function() {
         const tx = await this.nft.connect(this.normalUser).safeMintNft();
         const waitedTx = await tx.wait();
         expect(waitedTx.status).to.equal(1);
      });
});

当它达到这种情况时，我们将成本设置为0。1个以太币（账户normalUser拥有它，因为它是一个拥有999+以太币的安全帽账户）。当它到达it语句时，我得到这个错误：

Error: Transaction reverted: function call failed to execute
at MelkExp.safeMintNft (contracts/MelkExp.sol:107)

线107是contractAddress.transfer(nftCost);
任何想法？如果任何信息是失踪，我会编辑或在评论中回答