SERVICE UNAVAILABLE at REST API calling

My API route in routes/api.php file is like below.

Route::post('/register', [RegisterController::class, 'register']);

My register function of RegisterController is like below

public function register(RegistrationValidate $request)
    {
        $user = User::create([
            'username' => request('username'),
            'email' => request('email'),
            'full_name' => request('full_name'),
            'store_name' => request('store_name'),
            'store_logo' => $fileName,
            'password' => Hash::make(request('password')),            
        ]);

        $token = $user->createToken($this->clientToken())->accessToken;
        return response()->json([
            'user' => $user,
            'token' => $token,
        ], 201);
    }

I am getting SERVICE UNAVAILABLE error like below