Yes it was www, I replaced with [subdomain] as I’m new I only can post 2 links in post 
/var/www/curieuxdinfo.info is the root path, but there is two folders in. One for http (there’s nothing but a message as the site is non-ready) and one for https that only me can access (I auto-generated my certificate, thats why I’m trying now letsencrypt before letting everyone see the site). Letsencrypt command didn’t create any new folder.
I guess the problem is here : currently, in my virtual host, if the request correspond to http it is redirect to the folder where there is the current page (site not ready). If the request is https (and its me), it is redirect to the folder with the cms.
So it is impossible for letsencrypt to access /.well-known/acme-challenge/I8ho2HvBZ1TaIybrMcKMUu51j69tknm10CW-TianOB8 on my domain.
Do you have idea on how should I configure this ?