SupplyChain.sol

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

... 

// 1st step in supply chain process 
function produceItemByFarmer(
        uint256 _productCode,
        string memory _originFarmName,
        string memory _originFarmInformation,
        string memory _originFarmLatitude,
        string memory _originFarmLongitude,
        string memory _productNotes,
        uint256 _price
    )
        public
        onlyFarmer // check address belongs to farmerRole
    {
        address distributorID; // Empty distributorID address
        address retailerID; // Empty retailerID address
        address consumerID; // Empty consumerID address
        Item memory newProduce; // Create a new struct Item in memory
        newProduce.stockUnit = stockUnit; // Stock Keeping Unit (stockUnit)
        newProduce.productCode = _productCode; // Product Codegenerated by the Farmer, goes on the package, can be verified by the Consumer
        newProduce.ownerID = _msgSender(); // Metamask-Ethereum address of the current owner as the product moves through 8 stages
        newProduce.originFarmerID = _msgSender(); // Metamask-Ethereum address of the Farmer
        newProduce.originFarmName = _originFarmName; // Farmer Name
        newProduce.originFarmInformation = _originFarmInformation; // Farmer Information
        newProduce.originFarmLatitude = _originFarmLatitude; // Farm Latitude
        newProduce.originFarmLongitude = _originFarmLongitude; // Farm Longitude
        newProduce.productID = _productCode + stockUnit; // Product ID
        newProduce.productNotes = _productNotes; // Product Notes
        newProduce.productPrice = _price; // Product Price
        newProduce.productDate = block.timestamp;
        newProduce.productSliced = 0;
        newProduce.itemState = defaultState; // Product State as represented in the enum above
        newProduce.distributorID = distributorID; // Metamask-Ethereum address of the Distributor
        newProduce.retailerID = retailerID; // Metamask-Ethereum address of the Retailer
        newProduce.consumerID = consumerID; // Metamask-Ethereum address of the Consumer // ADDED payable
        items[_productCode] = newProduce; // Add newProduce to items struct by productCode
        uint256 placeholder; // Block number place holder
        Txblocks memory txBlock; // create new txBlock struct
        txBlock.FTD = placeholder; // assign placeholder values
        txBlock.DTR = placeholder;
        txBlock.RTC = placeholder;
        itemsHistory[_productCode] = txBlock; // add txBlock to itemsHistory mapping by productCode

        // Increment stockUnit
        stockUnit = stockUnit + 1;

        // Emit the appropriate event
        emit ProduceByFarmer(_productCode);
    }
    
    ...