Many to many attach doesn't work...

service_shop pivot table.sql

<?php

use Illuminate\Database\Schema\Blueprint;
use Illuminate\Database\Migrations\Migration;

class CreateServiceShopTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('service_shop', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('serviceId')->unsigned()->index();
            $table->foreign('serviceId')->references('id')->on('services')->onDelete('cascade');
            $table->integer('shopId')->unsigned()->index();
            $table->foreign('shopId')->references('id')->on('shops')->onDelete('cascade');
            $table->timestamps();
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::drop('service_shop');
    }
}

Shop.php

<?php
// The model php file  /app/Models/Shop.php
namespace App\Models;

use Illuminate\Database\Eloquent\Model;

class Shop extends Model
{
  public function services()
  {
      return $this->belongsToMany('\App\Models\Service','service_shop','serviceId','shopId')->withTimestamps();
  }
}

ShopController.php

//This file response to my api endpoint
//The important part:

        $shop = new \App\Models\Shop;
        $shop->shopId = $request->input('shop_id');
        $shop->language = $request->input('language');
        $shop->token = $request->input('token');
        $shop->save();
        $shop->services()->attach($service->id);
        
// But the attach method doesn't do a thing...