@mrmarkuz Thanks for the information, I’ll look into it. I hope it makes sense to me. 
Unfortunately, due to the older database programs I use, I cannot use Firebird 4 or Firebird 5. That’s why it was important for me to use the latest version I could still use, which was Firebird 3.x, so I used that for the module. If I were to update to the latest Firebird version, I wouldn’t be able to use it…
I’m not sure if the Community Certificate is necessary for the Firebird module, although many developers use this option. I see you haven’t certified all your modules either. What do you suggest?
The next step is to test the VPS with VPN and security settings. See Using NS8 on a virtual host with a VPS provider - #9 by steve
Thank you for your help