ldc-supportweb/app/Http/Requests/UpdateMessage.php

<?php

namespace App\Http\Requests;

use Illuminate\Foundation\Http\FormRequest;

class UpdateMessage extends FormRequest
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return boolean
     */
    public function authorize(): bool
    {
        /** @var \App\Models\User|null $user */
        $user = auth()->user();

        return auth()->check() && $user->isAdmin();
    }

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules(): array
    {
        /** @var \App\Models\User */
        $user = auth()->user();
        return [
            'message' => 'required|min:' . ($user->isAdmin() ? '5' : '20'),
        ];
    }
}