Parallels 11 activation on OSX 10.13.6 fails (Check your Internet connection)

Dear all,
there are already at least 2 similar threads with the same topic but without any solution so far.
I just completely reinstalled my iMac mid2011 from scratch (after reformatting the drives).
I used the latest OSX supported for that model which is 10.13.6 High Sierra (where Parallels 11 was running fine before I formatted the drives).
During the Parallels 11 installation process I was asked to enter my account data for activation.
It failed with the following error message: "Check your Internet connection". My internet connection is fine! I am just logged in in my Parallels account and downloaded my P11 copy from there (plus the license key).
I think Parallels has changed something with the activation servers (I faced the same issue with Adobe Lightroom 6, but there was a workaround for this).
Can you please support me and tell me how to activate my copy of Parallels 11 on OSX 10.13.6.? I payed for it and legally own it (without any expiration date)! I think I should be able to install and use it.
Thank you very much!

 

To make things clear. Product is "Parallels Desktop 11 for Mac". I entered correct mail-address and password for my parallels account. After confirmation - the error message "Check your Internet connection" appears.
From my experience with Adobe Lightroom 6 activation I think there it was related to an update of the Adobe activation servers to TLS 1.2.
Please Parallels Support - held the users with this activation issue. I am not alone.
Thanks again.

 

I already tried https://kb.parallels.com/124073 which exactly describes my problem. But after executing all the steps the problem still exists.

 

Also tried https://kb.parallels.com/en/113744. that has not solved the problem either.