invitationNFT.sol

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

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC721/ERC721.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Counters.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol";

contract NftExample is ERC721, Ownable {
    using Counters for Counters.Counter;
    Counters.Counter private _tokenIds;

    constructor() ERC721("ZION Invite NFTv0", "ZIONiv0.0") {}

    function mintNft(address receiver) external onlyOwner returns (uint256) {
        _tokenIds.increment();

        uint256 newNftTokenId = _tokenIds.current();
        _mint(receiver, newNftTokenId);

        return newNftTokenId;
    }

    function mintNftOwners(address receiver) external returns (uint256) {
        _tokenIds.increment();

        uint256 newNftTokenId = _tokenIds.current();
        _mint(receiver, newNftTokenId);

        require (balanceOf(msg.sender) >= 0);
        return newNftTokenId;
    }

}