Good morning, everyone!
The problem is solved !I have learned something new again... 🙂
Your link (https://prnt.sc/n3fl34) goes to the start page, which should keep the actual project secret... (index.html).
I had called the Jobmonster project under a wrong link
http://www.social-jobs-cologne.de/wp
If you call the PHP address, everything works 🙂
http://www.social-jobs-cologne.de/index.php
Thank you very much for your support and have a nice day.