I am trying to send push notification to my android device from server using firebase cloud messaging system. I was able to successfully register my device and token for my devi
Try to use 'to' instead of 'registration_ids'
Here is body data saved in postman history[i don't remember whether it works or not]:
{ "data": {
"score": "5x1",
"time": "15:10" }, "to" : "token_id"}
Check this script: If you want to do topic messaging
$url = "https://fcm.googleapis.com/fcm/send";
                $topic = "topic_name";
                $fields = array(
                    "to"                => "/topics/".$topic,
                    "data"              => $message,
                    "time_to_live"      => 30,
                    "delay_while_idle"  => true
                );
                $auth_key = "auth_key";
                $headers = array(
                    "Authorization: key=".$auth_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($ch, CURLOPT_SSL_VERIFYPEER, false);
                curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
                $result = curl_exec($ch);
Hope that help
Thanks much @Shubham for the solution.
Guys please use @Shubham's code for sending notifications to "Topics'
I have modified his code a bit to address Single recipient messaging. Here it goes
<?php
$url = "https://fcm.googleapis.com/fcm/send";
                $val = "<your recipient id>";
                $message = array("message" => "This is a test message from server");
                $fields = array(
                    "to"                => $val,
                    "data"              => $message,
                    "time_to_live"      => 30,
                    "delay_while_idle"  => true
                );
                $auth_key = "<Your auth key>";
                $headers = array(
                    "Authorization: key=".$auth_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($ch, CURLOPT_SSL_VERIFYPEER, false);
                curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
                $result = curl_exec($ch);
?>
to - Single recipient
registration_ids - multicast messages (Many recipients - should be in array)
This may not be the ideal solution from my end but it definitely works :)