problem with filament code

Hello friends, i have problem with code i try calculate the days between tow days in filament forms this is the code return $form ->schema([ Forms\Components\TextInput::make('name') ->required(), Forms\Components\DatePicker::make('start_date') ->label('Start Date') ->required() ->reactive(), Forms\Components\DatePicker::make('end_date') ->label('End Date') ->required() ->reactive() ->afterStateUpdated(function ($set, $state) {

                    $startDate = Carbon::parse($state['start_date'] ?? null);
                    $endDate = Carbon::parse($state['end_date'] ?? null);
                    
                    // Calculate days between only if both dates are valid
                    $daysBetween = $startDate && $endDate ? $endDate->diffInDays($startDate) : null;
                    $set('days_between', $daysBetween);
                }),
            Forms\Components\TextInput::make('days_between')
                ->label('Days Between')
                ->disabled()
                ->dehydrated(false),
        ]);

it is not working correctly can you help me