Ubuntu 16.04 - Nginx - Error Type: unauthorized / Detail: Invalid response

Server
2

Is the web root you specify correct ?

does the folder /var/www/gfelot exist ? or is it /var/www/gfelot.zyz ?

if you place a file at /var/www/gfelot/.well-known/acme-challenge/test can you reach it at gfelot.xyz/.well-known/acme-challenge/test ?