I have created a Laravel app in which I am integrated meta API as shown below.

 $this->client = new Client([
     'base_uri' => 'https://graph.facebook.com/',
 ]);
$endpoint = "v20.0/{$this->adAccountId}/insights";
      $params = [
      'access_token' => $this->accessToken,
      'fields' => 'spend,created_time',
      'level' => 'ad',
      'TIME_INCREMENT' => 'day',
        ];
$response = $this->client->get($endpoint, [
    'query' => $params
]);

Above code is working fine. Now I need a meta Webhook which give me data of whenever client spend on Facebook ads. and I don’t know whet to do next.

I have created a Webhook using below code

$client = new Client([
            'base_uri' => 'https://graph.facebook.com',
        ]);
        $endpoint = '/v20.0/APPID/subscriptions?access_token='.$accessToken;
        $response = $client->post($endpoint, [
            'object' => 'page', 
            'callback_url' => $callbackUrl,
            'fields' => 'leadgen',
            'verify_token' => $verifyToken 
        ]);

I tried above code but it show error on Oouth. I also tried to give APPID|APP_SECRET. It also give errorOAuthException. I also used same code in graph API explorer.