Error 404, Woops. Looks like this page doesn't exist. Or 400 - Template "lightslider.html.twig" is not defined.

[uldics]

I cannot get it to show a page. It is one of main pages, listed on the front/home page. It is accessible only by a permission iaw. Login plugin.
When I have in page code routable: false it shows 404, no logon attempt is made.
When I have in page code routable: true it shows 400 after logon.
I have tried putting the template in various places, but it still doesn't work. Not sure if that is the problem, or there is something wrong with the modular necessity to further configure manually, which could of course be done automatically.
The best result I got was by putting lightslider.html.twig into grav/user/themes/antimatter/templates. But then I just had a small top portion (header module) of one of my images I had placed in all three modules subfolders of the page.
It should be more clearly documented, what has to be moved where for what endresult. Or even better - scripted to be done at install or confugurable via admin interface.