Add `username` to the existing `App\Models\User` model's `$fillable` array (do not replace your existing model):

```php
protected $fillable = [
    // keep existing fields...
    'name',
    'username',
    'email',
    'password',
];
```

If the model already uses `$guarded = []`, no fillable change is needed. Keep password hashing behavior consistent with your existing Laravel User model.
