Laravel Sanctum SPA Authentication Not Working with Next.js Frontend

Problem

I'm building an application with a Next.js frontend and Laravel backend using Sanctum for SPA authentication. When I login from the Next.js app, I can see the authentication cookies being set in the browser, but subsequent requests to get user information return "unauthenticated" errors. NOTE: Everything is working in Postman correctly.

Environment

• Frontend: Next.js
• Backend: Laravel with Sanctum
• Authentication: Laravel Sanctum SPA Authentication
• Everything works correctly when testing in Postman

What I've Tried

The login process works fine, and I can confirm cookies are set in the browser after login. However, when I try to fetch the authenticated user information, I get "unauthorized" errors. I tried GET request at "/api/v1/user" in Postman and it works.

Code

My login function:

const baseUrl = process.env.NEXT_PUBLIC_BASE_URL;

async function fetchCsrfCookie() {
    await fetch(`${process.env.NEXT_PUBLIC_BASE_URL}/sanctum/csrf-cookie`, {
        method: 'GET',
        credentials: 'include',
    });
}

export const fetchSignIn = async (username: string, password: string) => {
    //   1) Init Sanctum
    await fetchCsrfCookie();

    // 2) Login
    const res = await fetch(`${baseUrl}/api/v1/login`, {
        method: 'POST',
        credentials: 'include',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ username, password, remember: true }),
    });
    if (!res.ok) {
        throw new Error('Login failed');
    }
    return res.json();
};

Fetch user function:

export const fetchAuthUser = async () => {
    try {
        const res = await fetch(`${process.env.NEXT_PUBLIC_BASE_URL}/api/v1/user`, {
            method: 'GET',
            credentials: 'include',
            headers: {
                'Content-Type': 'application/json',
            },
        });

        if (!res.ok) {
            const errorData: any = await res.json();
            console.error('Error data:', errorData);
            throw new Error(errorData.message || res.statusText);
        }

        return res.json();
    } catch (error) {
        console.error(`Failed to fetch resource:`, error);
        throw error;
    }
};