ldc-supportweb/app/Http/Requests/Bo/Users/FavouriteSiteRequest.php

<?php

namespace App\Http\Requests\Bo\Users;

use Illuminate\Validation\Rule;
use Illuminate\Support\Facades\Auth;
use Illuminate\Foundation\Http\FormRequest;

class FavouriteSiteRequest extends FormRequest
{
/**
 * Determine if the user is authorized to make this request.
 *
 * @return boolean
 */
    public function authorize(): bool
    {
        return Auth::check();
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules(): array
    {
        /** @var \App\Models\User|null $user */
        $user = Auth::user();

        return [
            'favourite_site_id' => [
                'nullable',
                'exists:sites,id',
                Rule::in($user->sites->pluck('id')),
            ],
        ];
    }
}