Morarible Buy Tokens getting error in marketPlace contract

Hello Guys,
I am following the tutorial but using Reactjs… and much completed just getting the error in buying nfts… when meta mask popup is opening it is showing transaction error : exception thrown in contract code

after confirming the transaction , item is removed from EthNFTOwners but not from the EthNFTTransfers… and also i am not getting what is EthNFTTransfers if somebody clear my concept…will be grateful for that as I didn’t know anything about blockchain before landing on this project…

console logging this error after completing the transaction

this is contract code…

//Contract based on
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "../node_modules/@openzeppelin/contracts/token/ERC721/IERC721.sol";

contract Marketplace {
    struct ProductItem{
        uint256 id;
        address tokenAddress;
        uint256 tokenId;
        address payable seller;
        uint256 price;
        bool purchased;
    ProductItem[] public products;

    mapping(address => mapping(uint => bool)) activeItems;

    event productCreated(uint256 id, uint256 tokenId, address tokenAddress, uint256 price);
    event productSold(uint256 id, address buyer, uint256 price);

    modifier OnlyItemOwner(address tokenAddress, uint256 tokenId){
        IERC721 tokenContract = IERC721(tokenAddress);
        require(tokenContract.ownerOf(tokenId) == msg.sender);

    modifier HasTransferApproval(address tokenAddress, uint256 tokenId){
        IERC721 tokenContract = IERC721(tokenAddress);
        require(tokenContract.getApproved(tokenId) == address(this));

    modifier ItemExists(uint256 id){
        require(id < products.length && products[id].id == id, "Could not find Item");

    modifier IsForSale(uint256 id){
        require(products[id].purchased == false, "Item is already sold");

    function itemAdded(uint256 tokenId, address tokenAddress, uint256 price) OnlyItemOwner(tokenAddress, tokenId) HasTransferApproval(tokenAddress, tokenId) external returns (uint256){
        require(activeItems[tokenAddress][tokenId] == false, "Item is already up for sale");
        uint256 newItemId = products.length;
        products.push(ProductItem(newItemId, tokenAddress, tokenId, payable (msg.sender), price, false));
        activeItems[tokenAddress][tokenId] = true;

        assert(products[newItemId].id == newItemId);
        emit productCreated(newItemId, tokenId, tokenAddress, price);
        return newItemId;

    function buyItem(uint256 id) payable external ItemExists(id) IsForSale(id) HasTransferApproval(products[id].tokenAddress, products[id].tokenId){
        require(msg.value >= products[id].price, "Not enough Funds sent");
        require(msg.sender != products[id].seller);

        products[id].purchased = true;
        activeItems[products[id].tokenAddress][products[id].tokenId] = false;
        IERC721(products[id].tokenAddress).safeTransferFrom(products[id].seller, msg.sender, products[id].tokenId);

        emit productSold(id, msg.sender , products[id].price);


and this is buy function

export const buyItems = async (tokenId,price) => {
    try {

        const web3 = await Moralis.Web3.enable();

        const currentUser = await Moralis.User.current();
        const userAddress = currentUser.get('ethAddress')

        const priceInWei = web3.utils.toWei(price,'ether')

        window.marketplaceContract = new web3.eth.Contract(marketplaceABI, marketplaceRemixAddress);
        const transfer = await window.marketplaceContract.methods.buyItem(tokenId).send({from:userAddress, value:priceInWei})

    } catch (error) {

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struct AuctionItem {
        uint256 id;
        address tokenAddress;
        uint256 tokenId;
        address payable seller;
        uint256 askingPrice;
        bool isSold;

    AuctionItem[] public itemsForSale;
    mapping (address => mapping (uint256 => bool)) activeItems;

I also just only followed tutorial and he explains contract for marketplace like that, i use those codes and it worked very well
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Most likely, you were using the same address to buy and sell the item. Please make sure you are using different address so that you assert statement doesn’t get called. The assert statement can have inbuilt messages so try to put them and debug to make sure.

Hope this helps. Thanks.

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Thank you… It helps me… :hugs:

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BTW… I wanna mention that the problem was in the buying function… I am providing tokenId instead of item uid that causing an error…
I found this in error, showing

item doesn’t exist

in ItemExists modifier :innocent::

Oh okay. That’s good to know.

Have a good day :slight_smile:

1 Like