This is my database schema:
```sql
CREATE TABLE `employees` (
	`id` INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
	`last_name` VARCHAR(800) NOT NULL,
	`first_name` VARCHAR(800) NOT NULL,
	`middle_name` VARCHAR(800),
	`email` VARCHAR(800),
	`IP` VARCHAR(800),
	`created_at` DATETIME NOT NULL,
    `updated_at` DATETIME
);

CREATE TABLE `departments` (
	`id` INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
	`name` VARCHAR(800) NOT NULL,
	`created_at` DATETIME NOT NULL,
    `updated_at` DATETIME
);

CREATE TABLE `department_employee` (
	`id` INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
	`employee_id` INT UNSIGNED NOT NULL,
	`department_id` INT UNSIGNED NOT NULL,
	`created_at` DATETIME NOT NULL,
    `updated_at` DATETIME,
    FOREIGN KEY (`employee_id`) REFERENCES `employees` (`id`) ON UPDATE CASCADE ON DELETE CASCADE,
    FOREIGN KEY (`department_id`) REFERENCES `departments` (`id`) ON UPDATE CASCADE ON DELETE CASCADE
);
```
Model "Employee":
```php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;

class Employee extends Model {
    protected $table = 'employees';
    public function departments(): BelongsToMany {
        return $this->belongsToMany(Department::class, 'department_employee', 'employee_id', 'department_id');
    }
}
```
Model "Department":
```php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsToMany;

class Department extends Model {
    protected $table = 'departments';
    public function employees(): BelongsToMany {
        return $this->belongsToMany(Employee::class, 'department_employee', 'department_id', 'employee_id');
    }
}
```
EmployeeResource.php
```php
<?php

namespace App\Filament\Resources;

use App\Filament\Resources\EmployeeResource\Pages;
use App\Filament\Resources\EmployeeResource\RelationManagers;
use App\Models\Employee;
use Filament\Forms;
use Filament\Forms\Form;
use Filament\Resources\Resource;
use Filament\Tables;
use Filament\Tables\Table;
use Illuminate\Database\Eloquent\Builder;
use Illuminate\Database\Eloquent\SoftDeletingScope;
use App\Models\Department;

class EmployeeResource extends Resource {
    protected static ?string $model = Employee::class;
    protected static ?string $navigationIcon = 'heroicon-o-rectangle-stack';
    protected static ?string $navigationLabel = 'Employees';
    protected static ?string $pluralModelLabel = 'Employees';
    protected static ?string $modelLabel = 'employee';
    protected static ?string $recordTitleAttribute = 'last_name';

    public static function form(Form $form): Form {
        return $form
            ->schema([
                Forms\Components\TextInput::make('last_name')
                    ->label('Last name')
                    ->required(),
                Forms\Components\TextInput::make('first_name')
                    ->label("First name")
                    ->required(),
                Forms\Components\TextInput::make('middle_name')
                    ->label('Middle name'),
                Forms\Components\TextInput::make('email')
                    ->label('Email')
                    ->email(),
                Forms\Components\TextInput::make('IP')
                    ->label('IP'),
                Forms\Components\Select::make('departments')
                    ->label('Department')
                    ->relationship('departments', 'name')
                    ->searchable(),
            ]);
    }

    public static function table(Table $table): Table {
        return $table
            ->columns([
                //
            ])
            ->filters([
                //
            ])
            ->actions([
                Tables\Actions\EditAction::make(),
            ])
            ->bulkActions([
                Tables\Actions\BulkActionGroup::make([
                    Tables\Actions\DeleteBulkAction::make(),
                ]),
            ]);
    }

    public static function getRelations(): arra {
        return [
            //
        ];
    }

    public static function getPages(): array {
        return [
            'index' => Pages\ListEmployees::route('/'),
            'create' => Pages\CreateEmployee::route('/create'),
            'edit' => Pages\EditEmployee::route('/{record}/edit'),
        ];
    }
}

```
What am I doing wrong here?