Update User Provider to your `config/auth.php` file

auth.php

<?php


    'guards' => [
        'web' => [
            'driver' => 'session',
            'provider' => 'firebase_users', /**** Change 'users' to 'firebase_users' ****/
        ],

        'api' => [
            'driver' => 'token',
            'provider' => 'firebase_users', /**** Change 'users' to 'firebase_users' ****/
        ],
    ],
    
    'providers' => [
        'users' => [
            'driver' => 'eloquent',
            'model' => App\User::class,
        ],
        
        
        /**** Add this firebase users provider ****/
        'firebase_users' => [
            'driver' => 'eloquent',
            'model' => Vinkas\Firebase\Auth\User::class,
        ],
        /**** ****/
        
    ],