API-1851: Event API: precise the URL target location can not be localhost

Author: tomglvng

content/events-api/subscription.md

@@ -19,6 +19,9 @@ Since your connected application will have only one Request URL, maybe you'll ne
 
 Your Request URL will receive JSON-based payloads containing wrapped event types.
 
+::: info
+For security reasons, local URLs cannot be used as Events API Request URL.
+:::
 
 ## Receive Events
 

content/getting-started/quick-start-my-first-webhook-5x/step-1.md

@@ -2,6 +2,10 @@
 
 Here, you will connect an event subscription to a fake endpoint and receive your first data. :rocket:
 
+::: info
+For security reasons, local URLs are blocked for event API target location and cannot be used as a fake endpoint. Use Mockbin or a comparable tool instead.
+:::
+
 ## Create a Bin on Mockbin
 
 [Mockbin](http://mockbin.org/) allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.