Raise exception on FAILED resposne from backend. Closes #8.

bigbluebutton/api/bigbluebutton.py

@@ -147,6 +147,14 @@ class BigBlueButton:
         except Exception as ex:
             raise BigBlueButtonError("Failed to parse XML response from backend.") from ex
 
+        if xml.get("returncode", "FAILED").upper() == "FAILED":
+            message_key = res.get("messageKey", "")
+            message = res.get("message", "Unknown error")
+
+            ex = BigBlueButtonError(f"Backend returned FAILED response: {message}")
+            ex.message_key = message_key
+            raise ex
+
         return xml["response"]
 
     def create_meeting(self, do_create: bool = True, *args, **kwargs) -> Meeting: