Issue Can't open/close Firewall ports

[Beinemann]

This seems a little bit odd but although Plesk tells me that Plesk Firewall is working fine it doesn't seem to work. Online port scanner / Nmap see things different, too.
I tried to open Port 9987 udp for incoming data for a Teamspeak server (after the Server software wasn't working correctly though it told me that it would/everything is running fine, Plesk says) and I see the applied rule in the Firewall rules list, but neither TS is working nor port scanner say the certain port is opened.
Modifying other rules won't work as well (even the scenario allowing all incoming traffic).
I am working with Plesk Obsidian 18.0.27 (Update 1 installed). Anyone has an idea what could cause this?

 

[Bitpalast]

If the port is clearly open in Plesk and it is still not open from the outside, look elsewhere. Many providers operate firewalls before their servers that cannot be configured from within Plesk but from within their server control panels. For example, OVH is using such firewalls. You need to open the port there, too.

 

[Beinemann]

Hi Peter, thanks for your answer! I will check this!

 

[Beinemann]

Provider says that Plesk + Linux (CentOS 7) is managing the firewall settings.