firebase messaging api php subscribe to topic 411 error - php

Question

I am trying to implement notifications into my web app. I have this php file in which I send notifications:
<?php
function sendGCM($title,$message, $id) {
$url = 'https://fcm.googleapis.com/fcm/send';
$fields = array (
'registration_ids' => array (
$id
),
"notification" => array(
"title" => $title,
"body" => $message,
"click_action" => "https://google.com"
)
);
$fields = json_encode ( $fields );
$headers = array (
'Authorization: key=' . $MY_KEY,
'Content-Type: application/json'
);
$ch = curl_init ();
curl_setopt ( $ch, CURLOPT_URL, $url );
curl_setopt ( $ch, CURLOPT_POST, true );
curl_setopt ( $ch, CURLOPT_HTTPHEADER, $headers );
curl_setopt ( $ch, CURLOPT_RETURNTRANSFER, true );
curl_setopt ( $ch, CURLOPT_POSTFIELDS, $fields );
$result = curl_exec ( $ch );
echo $result;
curl_close ( $ch );
}
?>
Now what I want to do is to send a notification to a topic instead of individual ids. On this page it shows how you can subscribe an id to a topic. Here is the function I created to do that:
function createTopic($topic,$id) {
$url = 'https://iid.googleapis.com/iid/v1/' . $id . '/rel/topics/' . $topic;
$headers = array (
'Authorization: key=MY_KEY'
);
$ch = curl_init ();
curl_setopt ( $ch, CURLOPT_URL, $url );
curl_setopt ( $ch, CURLOPT_POST, true );
curl_setopt ( $ch, CURLOPT_HTTPHEADER, $headers );
curl_setopt ( $ch, CURLOPT_RETURNTRANSFER, true );
$result = curl_exec ( $ch );
echo $result;
curl_close ( $ch );
}
I am getting this error from Google and I can't figure out what is going wrong:
That’s an error.
POST requests require a Content-length header. That’s all we know.
Any help?

Answer 1

The example in the documentation shows use of a Content-Length header:
https://iid.googleapis.com/iid/v1/nKctODamlM4:CKrh_PC8kIb7O...clJONHoA/rel/topics/movies
Content-Type:application/json
Content-Length: 0
Authorization:key=AIzaSyZ-1u...0GBYzPu7Udno5aA
Add that to your request:
$headers = array (
'Authorization: key=' . $MY_KEY,
'Content-Length: 0'
);