The 401 Unauthorized error or missing cookies when using Laravel Sanctum with React is likely due to CORS or CSRF issues. Ensure:

Laravel:

• .env: SESSION_DOMAIN=localhost, SANCTUM_STATEFUL_DOMAINS=localhost:5173, SESSION_SECURE_COOKIE=false
• cors.php: supports_credentials => true, allowed_origins => ['http://localhost:5173']
• api.php: Include /sanctum/csrf-cookie and auth:sanctum middleware

React (Axios):

import axios from 'axios';

const apiClient = axios.create({
    baseURL: 'http://127.0.0.1:8000',
    withCredentials: true,
    withXSRFToken: true,
});

const login = async (email, password) => {
    await apiClient.get('/sanctum/csrf-cookie');
    await apiClient.post('/login', { email, password });
    const user = await apiClient.get('/user');
    return user.data;
};

Check browser DevTools for XSRF-TOKEN and laravel_session cookies.