React – map is not a function when I use with axios

I am trying to display the list of authors from my API, I’ve created simple component, and am using axios. My API looks like this:

{
    "links": [
        {
            "rel": "self",
            "href": "http://localhost:8080/booker/api/authors"
        }
    ],
    "content": [
        {
            "authorId": 4,
            "firstName": "Tonyslav",
            "lastName": "Shamal",
            "webPage": "www.tonisha.gov",
            "dateCreated": "2021-12-15T11:58:28.829+00:00",
            "numberOfBooks": 13,
            "links": [
                {
                    "rel": "books",
                    "href": "http://localhost:8080/booker/api/books/author/4"
                }
            ]
        },
        {
            "authorId": 6,
            "firstName": "Georgio",
            "lastName": "Martinez",
            "webPage": "www.got.gov",
            "dateCreated": "2021-12-15T11:58:28.829+00:00",
            "numberOfBooks": 16,
            "links": [
                {
                    "rel": "books",
                    "href": "http://localhost:8080/booker/api/books/author/6"
                }
            ]
        }
}

And my React components looks like this:

import { useEffect, useState } from 'react';
import axios from 'axios';

const Authors = () => {
    const [authors, setAuthors] = useState([]);
    useEffect(() => {

        axios.get('http://localhost:8080/booker/api/authors')
            .then(res => {
                setAuthors(res.data);
            })
            .catch(err => console.log(err));
    }, []);

    return (
        <div>
            {authors.map(author => (
                <div className="card" key={author.content.authorId}>
                    {author.content.firstName}
                </div>
            ))}
        </div>
    );
}

export default Authors;

This is my error from the console

TypeError: authors.map is not a function

Can anybody try to help me with this, i can not solve this error.