Laravel Sanctum API: Authenticated user is null causing 500 error

I'm new to Laravel and building a backend API system from scratch using Laravel + Sanctum (no frontend yet, just Postman for now). I'm trying to create a simple authenticated API where each logged-in user (karyawan) can create a "transaksi" (transaction), and their id_karyawan (worker_id) is stored alongside the new record. Here’s what I’ve done so far:

1. I successfully implemented login using a custom model Karyawan.
2. Login returns a token, and I can use it with Authorization: Bearer in Postman.

what fails:

1. When I POST to /transaksi (to create new transaction), I get a 500 Internal Server Error.
2. Debugging shows that Auth::user() returns null — even though I’m using a valid token in the header.
3. Not even using GET return output. It always showed 500 internal server error. I suspect that's because of the middleware issues.

What I'm trying to do:

When a user is logged in and hits the POST /transaksi endpoint, I want to:

1. Automatically attach id_karyawan from the logged-in user.
2. Store it inside the transaksi table with other validated data.

Here is some highlight on my code that I suspect:

1. The login works but not for logout.

Route::post('/login', [AuthController::class, 'login']); Route::middleware('auth:sanctum')->post('/logout', [AuthController::class, 'logout']);

This return 500.

2. Routing for transaction using sanctum too.

Route::middleware('auth:sanctum')->group(function () {
    Route::get('/transaksi', [TransaksiController::class, 'index']);
    Route::post('/transaksi', [TransaksiController::class, 'store']);}

3.Here is codes from TransaksiController.php

$user = Auth::user();
if (!$user) {
    return response()->json([
        'message' => 'Unauthorized - Token tidak valid atau sudah expired',
        'debug' => [
            'auth_guard' => config('auth.defaults.guard'),
            'header_auth' => $request->header('Authorization'),
            'user_check' => Auth::check()
        ]
    ], 401);
}

Instead of return error or debug message, it keeps showing 500.

Let me know if you want to see:

AuthController (login/logout)

TransaksiController store method

routes/api.php

auth.php

I’ll provide them as needed.

I tried search and read the documentation but still can't figure it out. I'm sorry. Thank you for your help!