ERC-721 is the non-fungible token (NFT) standard for smart contracts.

In this tutorial, you will:

Create a simple ERC-721 collection contract that allows anyone to mint new non-fungible tokens in the collection.
Deploy the contract on the Fantom testnet through a node deployed with Chainstack.
Interact with the deployed contract.
See that you can register your collection on an NFT market.

Prerequisites

Chainstack account to deploy a Fantom node.
Truffle Suite to create and deploy contracts.
OpenZeppelin Contracts to use the audited ERC-721 libraries to create your ERC-721 collection contract.

Overview

To get from zero to a deployed ERC-721 contract on the Fantom testnet, do the following:

With Chainstack, create a public chain project.
With Chainstack, join the Fantom testnet.
With Chainstack, access your Fantom node credentials.
With OpenZeppelin, create an ERC-721 contract.
With Truffle, compile and deploy the contract through your Fantom node.

Step-by-step

Create the contract

On your machine, in the contract directory, initialize Truffle:

truffle init

This will generate the Truffle boilerplate structure:

.
├── contracts  
│   └── .gitkeep  
├── migrations  
│   └── .gitkeep  
├── test  
│   └── .gitkeep  
└── truffle-config.js

Go to the contracts directory. In the directory, create your ERC-721 contract Fantom721Collection.sol.

//SPDX-License-Identifier: MIT
pragma solidity ^0.8;

import "@openzeppelin/contracts/token/ERC721/extensions/ERC721URIStorage.sol";

contract Fantom721Collection is ERC721URIStorage {
    uint256 public tokenCounter;
    constructor () public ERC721 ("COLLECTION_NAME", "COLLECTION_TICKER"){
        tokenCounter = 0;
    }

    function createCollectible(string memory tokenURI) public returns (uint256) {
        uint256 newItemId = tokenCounter;
        _safeMint(msg.sender, newItemId);
        _setTokenURI(newItemId, tokenURI);
        tokenCounter = tokenCounter + 1;
        return newItemId;
    }

}

The contract implementation is the following:

The contract uses OpenZeppelin audited ERC-721 contract templates.
The contract is a mintable collection. Anyone can add a token to the collection through createCollectible.
COLLECTION_NAME — any name to give to your collection
COLLECTION_TICKER — any ticker for your collection

Create 2_deploy_contracts.js in the migrations directory.

module.exports = function(deployer) {
var Fantom721Collection = artifacts.require("./Fantom721Collection.sol");
  deployer.deploy(Fantom721Collection);
};

This will create the contract deployment instructions for Truffle.

Compile and deploy the contract

Install HDWalletProvider.

HDWalletProvider is Truffle's separate npm package used to sign transactions.

Run:
```
npm install @truffle/hdwallet-provider
```
Edit truffle-config.js to add:
- HDWalletProvider
- Your Fantom node access and credentials
- Your Fantom account that you will use to deploy the contract.
```
const HDWalletProvider = require("@truffle/hdwallet-provider");
const private_key = 'YOUR_PRIVATE_KEY';

module.exports = {
 networks: {
    testnet: {
        provider: () => new HDWalletProvider(private_key, "YOUR_CHAINSTACK_ENDPOINT"),
        network_id: 4002
    } 
   },

 compilers: {
    solc: {
    version: "0.8.9",
    }
  }
};
```
where
- testnet — any network name that you will pass to the truffle migrate --network command.
- HDWalletProvider — Truffle's custom provider to sign transactions.
- YOUR_PRIVATE_KEY — the private key of your Fantom account that will deploy the contract. The account must have enough FTM funds to run the deployment. See also Fantom testnet faucet.
- YOUR_CHAINSTACK_ENDPOINT — your Fantom node HTTPS endpoint deployed with Chainstack. See also View node access and credentials and Tools.
- network_id — the network ID of the Fantom network: mainnet is 250, testnet is 4002.
- solc — the Solidity compiler version that Truffle must use.
Run:
```
truffle migrate --network testnet
```
This will engage 2_deploy_contracts.js and deploy the contract to the Fantom testnet as specified in truffle-config.js.

Interact with the contract

Once your contract is deployed, you can view it online at FTMScan testnet.

For an easy way to interact with your deployed contract, verify it on FTMScan.

Flatten your contract code

Since your ERC-721 contract uses imported OpenZeppelin libraries, you must put all the imports into one .sol file to make FTMScan be able to verify it.

Install Truffle Flattener.

Run:
```
npm install truffle-flattener
```

Flatten the contract.

In the contracts directory, run:

npx truffle-flattener Fantom721Collection.sol > FlatFantom721Collection.sol

Clean up the licensing information.

The flattened contract will have the same licensing note imported from each of the files. Multiple licensing notes in one file break the FTMScan verification, so you have to leave one licensing note for the entirety of the flattened contract.

The easiest way to clean up is to search for the SPDX mentions in the file and remove all of them except for the very first one.

Verify the deployed contract on FTMScan

At this point, you have your flattened and cleaned-up contract ready for the FTMScan verification.

Go to FTMScan testnet.
Find your deployed contract. The address of your contract should have been printed by Truffle at the end of the deployment in the contract address field.
On the contract page on FTMScan, click Contract > Verify and Publish.
In Compiler Type, select Solidity (Single file).
In Compiler Version, select v0.8.9. This is the version this tutorial used to compile the contract.
In Open Source License Type, select MIT License (MIT).
Click Continue.
Keep the Optimization option set to No as Truffle does not use optimization by default.
Paste the entirety of your flattened .sol contract in the Enter the Solidity Contract Code below field.
Click Verify and Publish.

FTMScan will take a few seconds to compile your contract, verify, and publish it.

Interact with the contract

Now that your ERC-721 contract is verified, FTMScan is effectively a front-end instance for your contract.

Mint an NFT in the collection

You can use any account to call the createCollectible function.

Make sure you have:

MetaMask installed and unlocked as you will need it to call the contract. See Fantom tooling: MetaMask.
Testnet FTM on the account to pay for the transaction. See Fantom testnet faucet.

On FTMScan, on your contract, click Contract.
Click Write Contract.
Click Connect to Web3.
Under createCollectible, in the tokenURI field, provide any string to serve as metadata for this specific NFT. See also OpenZeppelin ERC-721 for a metadata example.
Click Write.

This will send a transaction to mint in NFT in your contract collection and distribute the token to the account called createCollectible.

Check the balances

Check the NFT balance of an address:

On FTMScan, on your contract, click Contract.
Click Read Contract.
Scroll to the balanceOf field.
In the owner (address) field, provide the address of the account you used to deploy the contract.
Click Query.

Check the number of minted NFTs

On FTMScan, on your contract, click Contract.
Click Read Contract.
Check the tokenCounter field.

Listing on an NFT market

Having gone through the tutorial to understand the basics of creating an NFT collection, you can amend the contract to your needs and deploy it on the Fantom mainnet.

Once deployed, you can list the collection at an NFT marketplace—Artion.

See Artion: Register Collection.