Add recipientNotProvided() exception.

src/Exceptions/CouldNotSendNotification.php

@@ -54,4 +54,14 @@ public static function messageButtonsLimitExceeded()
     {
         return new static('You cannot add more than 3 buttons in 1 notification message.');
     }
+
+    /**
+     * Thrown when there is no user id or phone number provided.
+     *
+     * @return static
+     */
+    public static function recipientNotProvided()
+    {
+        return new static('Facebook notification recipient ID or Phone Number was not provided. Please refer usage docs.');
+    }
 }

src/FacebookChannel.php

@@ -5,6 +5,7 @@
 use NotificationChannels\Facebook\Events\MessageWasSent;
 use NotificationChannels\Facebook\Events\SendingMessage;
 use Illuminate\Notifications\Notification;
+use NotificationChannels\Facebook\Exceptions\CouldNotSendNotification;
 
 class FacebookChannel
 {
@@ -40,7 +41,7 @@ public function send($notifiable, Notification $notification)
 
         if ($message->toNotGiven()) {
             if (! $to = $notifiable->routeNotificationFor('facebook')) {
-                return;
+                throw CouldNotSendNotification::recipientNotProvided();
             }
 
             $message->to($to);