diff --git a/README.md b/README.md
index 3a56706..816e227 100644
--- a/README.md
+++ b/README.md
@@ -75,6 +75,7 @@ Options:
 409 | conflict | number is from unsupported country
 409 | conflict | number is from unsupported telco
 409 | conflict | Wrong phone number format
+409 | conflict | Unknown sender ID(name) – the sender ID used is not recognized or not registered with the SMS provider even if the token is correct
 
 - An example of a successfully sent SMS.