diff --git a/src/OneSignalClient.php b/src/OneSignalClient.php
index a9bae1a..41ec5ea 100644
--- a/src/OneSignalClient.php
+++ b/src/OneSignalClient.php
@@ -230,6 +230,11 @@ public function sendNotificationToExternalUser($message, $userId, $url = null, $
             );
         }
 
+        // Make sure to select channel as "Push" with parameter "channel_for_external_user_ids"
+        if (!isset($params['channel_for_external_user_ids'])) {
+            $params['channel_for_external_user_ids'] = "push";
+        }
+
         $this->sendNotificationCustom($params);
     }
     public function sendNotificationUsingTags($message, $tags, $url = null, $data = null, $buttons = null, $schedule = null, $headings = null, $subtitle = null) {