Greetings to all React developers out there, especially the newbies like me. I am currently facing an issue with implementing react-modal in my React Component based on this example here. Unfortunately, I have encountered several errors that are proving difficult for me to resolve.

import React, {useState} from 'react';
import {
  Card, Button, CardImg, CardTitle, CardText, CardGroup,
  CardSubtitle, CardBody, CardFooter, CardHeader, CardColumns, CardDeck
} from 'reactstrap';
import Config from 'config';
import parse from 'html-react-parser';
import "./Item.css";
import ReactDOM from 'react-dom';
import Modal from 'react-modal';

const customStyles = {
    content: {
        top: '50%',
        left: '50%',
        right: 'auto',
        bottom: 'auto',
        marginRight: '-50%',
        transform: 'translate(-50%, -50%)',
    },
};

//Modal.setAppElement('FeaturedCards');

class FeaturedItems extends React.Component {
    constructor() {
        super();
        this.state = {
            name: 'React',
            apiData: [],
        };
    }

    async componentDidMount() {
        const tokenString = sessionStorage.getItem("token");
        const token = JSON.parse(tokenString);

        let headers = new Headers({
            "Accept": "application/json",
            "Content-Type": "application/json",
            'Authorization': 'Bearer ' + token.token
        });

        const response = await fetch(Config.apiUrl + `/api/Items/GetFeaturedItems`, {
            method: "GET",
            headers: headers
        });
        const json = await response.json();
        console.log(json);
        this.setState({ itemList: json });
    }

    render() {
        const [modalIsOpen, setIsOpen] = useState(false);
        const items = this.state.itemList;
        let subtitle;

        function handleClick(item) {
            console.log('this is:', item);
            setIsOpen(true);
        }

        function afterOpenModal() {
            // references are now sync'd and can be accessed.
            subtitle.style.color = '#f00';
        }

        function closeModal() {
            setIsOpen(false);
        }

        var formatter = new Intl.NumberFormat('en-US', {
            style: 'currency',
            currency: 'USD'            
        });

        return (
            <div>
                <CardColumns>
                    {items && items.map(item =>
                        <>
                            <Card key={item.itemNumber} tag="a" onClick={() => handleClick(item)} style={{ cursor: "pointer" }}>
                                <CardHeader tag="h3">Featured</CardHeader>
                                <CardImg top className="card-picture" src={"data:image/png;base64," + item.images[0]?.ImageData)} id={item.itemNumber + "Img"} alt={item.itemNumber} />
                                <CardBody className="card-body">
                                    <CardTitle tag="h5">{item.itemNumber}</CardTitle>
                                    <CardSubtitle tag="h6" className="mb-2 text-muted">{item.categoryName}</CardSubtitle>
                                    <CardText className="card-description">{item.itemDescription}</CardText>
                                </CardBody>
                                <CardFooter className="text-muted">{formatter.format(item.price)}</CardFooter>
                            </Card>
                            <Modal
                                isOpen={modalIsOpen}
                                onAfterOpen={afterOpenModal}
                                onRequestClose={closeModal}
                                style={customStyles}
                                contentLabel="Example Modal">
                                    <h2 ref={(_subtitle) => (subtitle = _subtitle)}>Hello</h2>
                                    <button onClick={closeModal}>close</button>
                                    <div>I am a modal</div>
                                    <form>
                                        <input />
                                        <button>tab navigation</button>
                                        <button>stays</button>
                                        <button>inside</button>
                                        <button>the modal</button>
                                    </form>
                            </Modal>
                        </>
                    )}                
                </CardColumns>
            </div>
        );
    }
}
export default FeaturedItems;

I seem to be stuck with a few errors:

1. Where exactly should

   const [modalIsOpen, setIsOpen] = useState(false)

   be placed to prevent encountering Error: Invalid hook call?
2. How should I use

   Modal.setAppElement('FeaturedCards')

   , because it does not work with FeaturedCards?

Your assistance on this matter will be greatly appreciated.