Magic Spam can not be installed through Plesk

[Centauri2k]

Hello, I can not install Magic Spam through Plesk. It always comes to error message:

Fehler bei der Installation der Erweiterung
Execution of /opt/psa/tmp/module8hccLn/plib/scripts/pre-install.php failed with exit code 1 and the output:
Error connecting to localhost port 8443: 111
API admin port 8443 is not accessible from 127.0.0.1. This is normally the result of an unintended firewall rule. Please check your firewall settings and add 127.0.0.1 to the 'permitted' to connect list accordingly.

My firewall is not configured. I have imported an empty accept policy:

Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination

What can I do?

I have purchased a valid MagicSpam license through Plesk

My Server:
‪Debian 8.10‬
Plesk Onyx Version 17.5.3 Update #40

THX!

[magicspam]

Hello Centauri2k,

Thank you for your post.

From your email we understand that you were unable to install MagicSpam due to connection issue to port 8443 from your localhost.

In order to start troubleshooting this issue, can you please let us know if you have SELinux or CageFS in your system that would prevent the access from 127.0.0.1?

In order to test if the SELinux or CageFS are enabled on your system, could you please send us outputs of the following commands:

For SELinux:

sestatus -v

and for CageFS:

/usr/sbin/cagefsctl --cagefs-status
/usr/sbin/cagefsctl --list-enabled

Please let us know if you have any questions in the meantime.