Mysql – Register page with "TypeError: Cannot read properties of undefined (reading 'data') at handleClick". What is the problem here?

I created a register page, in which I have the inputs email, password, first name, and last name. Upon clicking the "Register" button, I received an error message that says "TypeError: Cannot read properties of undefined (reading ‘data’) at handleClick". What is the problem here?

Below is my code:

import { useState } from "react";
import "./register.scss";
import axios from "axios";

const Register = () => {
    const [inputs, setInputs] = useState({
        email: "",
        password: "",
        firstName: "",
        lastName: "",
    });

    const [err, setErr] = useState(null);

    const handleChange = (e) => {
        setInputs(prev => ({...prev, [e.target.name]: e.target.value}));
    };

    const handleClick = async e => {
        e.preventDefault();
    
        try{
          await axios.post("http://localhost:8800/api/auth/register", inputs);
        } catch (err) {
          setErr(err.response.data);
        }
    };

    console.log(err);

    return (
        <div className="register-page">
            <form>
                <input type="email" placeholder="Email" name="email" onChange={handleChange} />
                <input type="password" placeholder="Enter Password" name="password" onChange={handleChange} />
                <input type="text" placeholder="First Name" name="firstName" onChange={handleChange} />
                <input type="text" placeholder="Last Name" name="lastName" onChange={handleChange} />
                {err && err}
                <button onClick={handleClick}>Register</button>
            </form>
        </div>
    )
};

export default Register;

If everything works normally, I should be able to see the email, password, first name, and last name posted onto the backend server table on MySQL.