After the installation, there is the error: Sorry: we will be back soon

I followed this guide and finally finished overcoming the DB access errors, as per my fix reported in this post.
Unfortunately by completing it I am once again at a full stop.
After the command bench --site install-app erpnext, the latest commands are:

sudo apt install nginx
bench setup nginx
rm -f /etc/nginx/sites-enabled/*
sudo ln -s /home/my_user/frappe-bench/config/nginx.conf /etc/nginx/sites-enabled/frappe.conf
sudo service nginx restart

Then, whit the result is a page with Sorry: we will be back soon.

I have seen other messages about this error, but I don’t understand why I have to reinstall the application as I followed the instructions step by step.

Anyway, the command
bench --site install-app erpnext
does not solve the problem.

Please can I get some help?

try to check file “common_site_config.json” in sites folder, “maintenance_mode” should be 0. I had the same problem and this was the solution.

No, it is not a solution.
Arrive at login, enter Administrator / Password and return to “Sorry …”:
I refresh the page and there is the message “Internal Error”.

I am very disappointed.