This response means that the response from the client application that does not start with a CON or an END. This includes empty responses or ones that start with spaces before the CON or END.
CON means an intermediate menu; Or that the session is CONtinuing
END means the final menu and will trigger session termination. i.e the session is ENDing
The expected client response is a string containing the menu to be displayed on the user’s phone. This menu should always start with CON or an END. Here's an example:
$response = "CON Which service would you like to subscribe to?\n";
$response .= "1. Betting Tips \n";
$response .= "2. Bible Verses";