Captive Portal - External splash page and creating error message

We are using a Balance One with captive portal and external splash page. When a user enters their ‘Guest Code’ on the portal incorrectly, the page refreshes to a fully blank page (all white) on the browser with no message to the user indicating a problem (the end of the URL indicates a failed login attempt). We need to have something like this generated (from a different mfg router) -

Here is a sample URL when an incorrect ‘Guest Code’ is entered -

This is the message I received from our programmer that operates the Radius server we use for authentication - ***We will need some documentation from Peplink on whether they support error message during authentication. Basically Peplink needs to parse the response from our RADIUS server and allow us to display that on the captive portal.

***How can we create an error message to the user that an incorrect Guest Code was entered?
Thank you for your help.


Please refer to this (Peplink | Pepwave - Forum) link. The required attributes were there.

Hope this help.