[SOLVED] Unable to install the application

I don't know about your DNS configuration, but it may be the source of the issue.
You access to www.projeqtor.fr. As long as your local DNS resolve it as local IP, it can work, otherwise you'll be redirected to our servers (we own projeqtor.fr domain name)

To try and identify issue, open browser dev tool, on network tab.
When error occirs, select request on error and check response part.
We should have interesting information here.

Error is exactly what I previously guessed :
host=www.projeqtor.fr => "your" internal subdomain
host " www.projeqtor.fr " (62.210.78.152) : our IP. Our servers won't reply to your requests

So you have dns resolution errors.
Try and change your domain name to something that really belongs to you, something like projeqtor.yourdomain.com