cURL_init() stops the program from running - php

Question

I have added the .php files on my server to send the notifications using FCM, but the code stops running when I create the actual message. I have a constructor for push and when I call it in sendSinglePush, it does not do anything.
The rest is working properly. I get the parameters ok, and the devicetoken. I just need to create that push and it should work. I've used the same sendSinglePush.php for testing on localhost, and it works. When I add it on server it just stops.
EDIT: As per #ADyson, who helped me understand abit about logging my errors, I started to log every variable from the start to the point where it crashes. The $push it's alright, the problem it's on Firebase.php:
<?php
class Firebase {
public function send($registration_ids, $message) {
$fields = array(
'registration_ids' => array($registration_ids),
'data' => $message,
);
//print_r($fields);
return $this->sendPushNotification($fields);
}
/*
* This function will make the actuall curl request to firebase server
* and then the message is sent
*/
private function sendPushNotification($fields) {
//importing the constant files
require_once 'Config.php';
//firebase server url to send the curl request
$url = 'https://fcm.googleapis.com/fcm/send';
//building headers for the request
$headers = array(
'Authorization: key=' . FIREBASE_API_KEY,
'Content-Type: application/json'
);
//Initializing curl to open a connection
$ch = curl_init();
print_r(curl_error($ch));
//Setting the curl url
curl_setopt($ch, CURLOPT_URL, $url);
//setting the method as post
curl_setopt($ch, CURLOPT_POST, true);
//adding headers
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
//disabling ssl support
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
//adding the fields in json format
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
//finally executing the curl request
$result = curl_exec($ch);
print_r($result);
if ($result === FALSE) {
die('Curl failed: ' . curl_error($ch));
print_r(curl_error($ch));
}
//Now close the connection
curl_close($ch);
//and return the result
return $result;
}
}
And the methods are called from sendSinglePush.php, where all the variables are sent correctly:
$mPushNotification = $push->getPush();
//print_r($mPushNotification);
//getting the token from database object
$devicetoken = $db->getTokenByEmail($_POST['email']);
//print_r($devicetoken);
//creating firebase class object
$firebase = new Firebase();
//sending push notification and displaying result
$firebase->send($devicetoken, $mPushNotification);
I have added different print_r() to check the output using POSTMAN and, from that code, the $headers are fine, after the $ch = curl_init(); nothing else shows up. I tried to add print_r(curl_error($ch)); but it does not show enything. Also, I tried with print_r(1); under the $ch = curl_init();to see if the code keeps running, but on postman there was no answer, only a blank screen and 500 Internal Server Error.