voucher/app/Http/Controllers/Api/CustomerLevelController.php

<?php

namespace App\Http\Controllers\Api;

use App\Http\Controllers\Controller;
use App\Models\CustomerLevel;
use Illuminate\Http\Request;

class CustomerLevelController extends Controller
{
    public function index(Request $request)
    {
        $query = CustomerLevel::query();

        if ($request->get('only') != '') {
            $query->whereIn('key', $request->get('only'));
        }

        return $query->get();
    }
}