How can I send a Firebase Cloud Messaging notification without use the Firebase Console?

Question

Firebase Cloud Messaging has a server-side APIs that you can call to send messages. See https://firebase.google.com/docs/cloud-messaging/server.

Sending a message can be as simple as using curl to call a HTTP end-point. See https://firebase.google.com/docs/cloud-messaging/server#implementing-http-connection-server-protocol

curl -X POST --header "Authorization: key=<API_ACCESS_KEY>" \
    --Header "Content-Type: application/json" \
    https://fcm.googleapis.com/fcm/send \
    -d "{\"to\":\"<YOUR_DEVICE_ID_TOKEN>\",\"notification\":{\"title\":\"Hello\",\"body\":\"Yellow\"}}"

This works using CURL

function sendGCM($message, $id) {


    $url = 'https://fcm.googleapis.com/fcm/send';

    $fields = array (
            'registration_ids' => array (
                    $id
            ),
            'data' => array (
                    "message" => $message
            )
    );
    $fields = json_encode ( $fields );

    $headers = array (
            'Authorization: key=' . "YOUR_KEY_HERE",
            '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 );
}

?>

$message is your message to send to the device

$id is the devices registration token

YOUR_KEY_HERE is your Server API Key (or Legacy Server API Key)

Use a service api.

URL: https://fcm.googleapis.com/fcm/send

Method Type: POST

Headers:

Content-Type: application/json
Authorization: key=your api key

Body/Payload:

{ "notification": {
    "title": "Your Title",
    "text": "Your Text",
     "click_action": "OPEN_ACTIVITY_1" // should match to your intent filter
  },
    "data": {
    "keyname": "any value " //you can get this data as extras in your activity and this data is optional
    },
  "to" : "to_id(firebase refreshedToken)"
} 

And with this in your app you can add below code in your activity to be called:

<intent-filter>
    <action android:name="OPEN_ACTIVITY_1" />
    <category android:name="android.intent.category.DEFAULT" />
</intent-filter>

Also check the answer on Firebase onMessageReceived not called when app in background

Examples using curl

Send messages to specific devices

To send messages to specific devices, set the to the registration token for the specific app instance

curl -H "Content-type: application/json" -H "Authorization:key=<Your Api key>"  -X POST -d '{ "data": { "score": "5x1","time": "15:10"},"to" : "<registration token>"}' https://fcm.googleapis.com/fcm/send

Send messages to topics

here the topic is : /topics/foo-bar

curl -H "Content-type: application/json" -H "Authorization:key=<Your Api key>"  -X POST -d '{ "to": "/topics/foo-bar","data": { "message": "This is a Firebase Cloud Messaging Topic Message!"}}' https://fcm.googleapis.com/fcm/send

Send messages to device groups

Sending messages to a device group is very similar to sending messages to an individual device. Set the to parameter to the unique notification key for the device group

curl -H "Content-type: application/json" -H "Authorization:key=<Your Api key>"  -X POST -d '{"to": "<aUniqueKey>","data": {"hello": "This is a Firebase Cloud Messaging Device Group Message!"}}' https://fcm.googleapis.com/fcm/send

Examples using Service API

API URL : https://fcm.googleapis.com/fcm/send

Headers

Content-type: application/json
Authorization:key=<Your Api key>

Request Method : POST

Request Body

Messages to specific devices

{
  "data": {
    "score": "5x1",
    "time": "15:10"
  },
  "to": "<registration token>"
}

Messages to topics

{
  "to": "/topics/foo-bar",
  "data": {
    "message": "This is a Firebase Cloud Messaging Topic Message!"
  }
}

Messages to device groups

{
  "to": "<aUniqueKey>",
  "data": {
    "hello": "This is a Firebase Cloud Messaging Device Group Message!"
  }
}

As mentioned by Frank, you can use Firebase Cloud Messaging (FCM) HTTP API to trigger push notification from your own back-end. But you won't be able to

1. send notifications to a Firebase User Identifier (UID) and
2. send notifications to user segments (targeting properties & events like you can on the user console).

Meaning: you'll have to store FCM/GCM registration ids (push tokens) yourself or use FCM topics to subscribe users. Keep also in mind that FCM is not an API for Firebase Notifications, it's a lower-level API without scheduling or open-rate analytics. Firebase Notifications is build on top on FCM.