diff --git a/autogpt/app.py b/autogpt/app.py
index eca0e0b7..3166e70d 100644
--- a/autogpt/app.py
+++ b/autogpt/app.py
@@ -263,11 +263,8 @@ def message_agent(key: str, message: str) -> str:
     # Check if the key is a valid integer
     if is_valid_int(key):
         agent_response = AGENT_MANAGER.message_agent(int(key), message)
-    # Check if the key is a valid string
-    elif isinstance(key, str):
-        agent_response = AGENT_MANAGER.message_agent(key, message)
     else:
-        return "Invalid key, must be an integer or a string."
+        return "Invalid key, must be an integer."
 
     # Speak response
     if CFG.speak_mode: