diff --git a/content/self-host/client-configuration/_index.en.md b/content/self-host/client-configuration/_index.en.md
index 8312ab0..52d98ec 100644
--- a/content/self-host/client-configuration/_index.en.md
+++ b/content/self-host/client-configuration/_index.en.md
@@ -47,7 +47,7 @@ As a `Pro` user you will be able to retrieve the `Key` from the [web console](ht
 
 This is for `Pro` user only. When you can log in on web console, but fail to log in on RustDesk client, it probably you have not set `API Server` correctly.
 
-If your API Server does not run on default `21114` port, please specify `API Server` explicitly.
+If your API Server does not run on default `21114` port (you may not add this port to firewall if you come from open source version), please specify `API Server` explicitly.
 e.g. your API Server runs on default https port, please specify `API Server` with `https://hbbs.example.com`.
 
 If you still can not confirm the value of `API Server`, please go to the welcome page of web console, the `API Server` is shown in above picture (The input box with `API:` label).