Can’t access /glotpress or change it to any other value

Hi

I’ve been trying to set up the plugin and so far everything works as expected except one little thing. If we can jump over this hurtle, it will be perfect.

Basically, I want to be able to access GP interface via domain.com/custom link.
I’ve read the manual which says i can add

define('GP_URL_BASE', '<your-path-here>');

but that doesn’t seem to work.
Also, I can’t access /glotpress even if I don’t touch wp-config.php file at all.

The only thing that is working as expected is

define('GP_URL_BASE', '/');

which made GP to be the frontpage of the site, but that completely hijacks the WordPress rendering, and if i try to open any other WP page, it loads GP saying nothing found here.

My permalinks are set to “Post Name”

The page I need help with: [log in to see the link]