Fecebook Messenger Bot in PHP doesn't always respond to user

Question

I have relatively simple Facebook Messenger bot in php for research purposes:

$access_token = "xxxxxxx";
$challenge = $_REQUEST['hub_challenge'];
$verify_token = $_REQUEST['hub_verify_token'];

if ($verify_token === 'MY_VERIFICATION_TOKEN') {
  echo $challenge;
}

$input = json_decode(file_get_contents('php://input'), true);

$sender = $input['entry'][0]['messaging'][0]['sender']['id'];
$message = $input['entry'][0]['messaging'][0]['message']['text'];

$url = 'https://graph.facebook.com/v2.6/me/messages?access_token='.$access_token.';

$ch = curl_init($url);

if($message=="hi")
{
        $jsonData = '{
        "recipient":{
                "id":"'.$sender.'"
        },
    "message":{
            "text":"hello!"
    }
    }';
}

$jsonDataEncoded = $jsonData;

curl_setopt($ch, CURLOPT_POST, 1);

curl_setopt($ch, CURLOPT_POSTFIELDS, $jsonDataEncoded);

curl_setopt($ch, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));

$result = curl_exec($ch);

and my cron job is same as in developer guide

curl -ik -X POST "https://graph.facebook.com/v2.6/me/subscribed_apps?access_token=xxxxxx"

So basically, nothing besides connection and one response. When i personally send "hi" (as a page owner and app owner), my bot always responds correctly, but when other people try to say hi - bot sometimes responds, sometimes not (usually not, in 5 cases bot responded once)

Additionally, when i visit my script url, it gives me error:

{"error":{"message":"(#100) The parameter recipient is required","type":"OAuthException","code":100,"fbtrace_id":"DvrO1UEw5BJ"}}

Please help me to set this right.

Answer 1

This might also happen if you forget to set the content-type as well.

Answer 2

Only users listed as Admins or Developers or Testers in your app roles (https://developers.facebook.com/apps/YOUR_APP_ID/roles/) can interact with your chat bot webhook. It won't be available to other users unless your app is approved by Facebook and publicly available. From the Docs:

When you're ready to release your app to the public, it must go through an approval process. This will walk you through the submission process and also acceptable and unacceptable usage.

About your second question, Facebook sends an API call to your webhook in the form of JSON data which includes sender id & recipient id in the HTTP request body. But when you visit your webhook manually, you don't have those parameters in your request body so $sender will be empty in your case. And that's why the CURL request to Facebook API fails with the error "The parameter recipient is required" because "recipient":{"id":"'.$sender.'"}, will be empty.

If you want to try your webhook manually, use actual recipient id, something like:

Curl Command:

curl -i -X POST -H 'Content-Type: application/json' -d '{"object":"page","entry":[{"id":43674671559,"time":1460620433256,"messaging":[{"sender":{"id":853241244787916},"recipient":{"id":43674671559},"timestamp":1460620433123,"message":{"mid":"mid.1460620432888:f8e3412003d2d1cd93","seq":12604,"text":"Testing Chat Bot .."}}]}]}' https://YOUR_WEBHOOK_URL_HERE