[pmwiki-users] Https and ShortUrl

[kirpi at kirpi.it]

Perhaps there might be some issue related to the www. prefix.
I tried and change something in the .htaccess file[1][2]

   RewriteEngine on
   RewriteCond %{HTTP:X-Forwarded-Proto} !https
   RewriteCond %{REQUEST_SCHEME} http [OR]
   RewriteCond %{HTTP_HOST} !^www\.
   RewriteRule ^ https://www.example.com%{REQUEST_URI} [NE,L,R=301]

as well as this in config.php
   $ShortUrlPrefix = 'https://www.example.com/s';

but I still get
   PmWiki can't process your request
   ShortUrl error: can't read code map

Is there any tool to trace where the issue might be hidden, please?
Thanks!

Luigi

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[1] http://stackoverflow.com/questions/13977851/htaccess-redirect-to-https-www
[2] I confess that I am not exactly understanding what I am doing...