Cloudflare ServerShield v 1.9.1 not working on Plesk 17.8.11

Hi there!

I've installed the ServerShield Extension, it's enabled, but i can't activate it, nor i get any error.
The Page simply reloads`if i click on activate without host key.

Server: Ubuntu Server 18.04.1 LTS
Plesk: 17.8.11
Servershield: 1.9.1

Did i miss something?

Greetings
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