ISPManager securing with SSL not working

[Hostingram]

Hello,
I'm trying to secure my ISPManager and BIllManager Panels with LetsEncrypt SSL.
Unfortunately I got a error:

https://server01.hostingram.net:1500/ispmgr

You can see here when you click to the error that the *.justinstalledpanel.com is blocking my certificate.

I searched in forums and found this: https://forum.ispsystem.com/showthread.php?p=8922
Also tried this: https://doc.ispsystem.com/index.php/Hosting_Beginner_Guide:_Configure_BILLmanager_addr ess
But unfortunately it's not working for me. Can you help me with this issue?

Thanks in advance.

Kind regards,
Metin