Nginx + PHP-FPM Error: This Page is Temporarily Unavailble

[shawn_a]

I dont know, I would start over and chmod everything to 777 before trying to install.

If I had to guess your owner of your files are not in the same group as php and php is not having any success creating necessary files, maybe you can chown them instead also.

sitename, comes from a hidden field in setup which guesses it from
all kinds of stuff

I have never seen setup fail at this stage before.