admin navigation links not opening pages. What URLs should I use (ngrok dev system)?

[den232]

Newbie here ... I'm trying to add admin links but cannot guess how to spell the addresses.   The admin link page begins all my links with the ngrok base address

https://088a-108-**-***-***.ngrok.io/

If I add nothing at all to this, the link works and loads the index.js page at https://088a-108-**-***-***.ngrok.io/pages.index.js 

For example, I have a page pages/newpage.js at https://088a-108-**-***-***.ngrok.io/pages/newpage.js

Everything else I try gets me a 404 error.

I've tried adding: 

1. newpage.js
2. pages/newpage.js
3. newpage
4. pages/newpage

and ...

1. newpage.txt
2. pages/newpage.txt
3. newpage.html
4. pages/newpage.html

I even tried to access my existing and functional page at pages/index.js, but can only access it by leaving the field blank.

Except for a blank URL field, I invariably get the message:

Application error: a client-side exception has occurred (see the browser console for more information).

Please advise.   Thanks! jb