C6300

> What mobile app do i use for C6300?

   I don't know.  I'd use a web browser.

> Why can't i access directly with routerlogin.net?

   I don't know.  What happens when you try?

   A useful problem description would include an accurate, detailed
description of what you did, and of what happened when you did it.  As
usual, showing actual actions (commands) with their actual results
(error messages, LED indicators, ...) can be more helpful than vague
descriptions or interpretations.