Hi @AlbinaBlazhko,
Thanks for reaching out!
I believe the issue you may have been having with getting an SSL Certificate is that you have both External DNS and Netlify DNS configured for theumdenken.com.
This can cause issues with getting an SSL certificate provisioned from Let’s Encrypt.
I do see that you’ve added a custom SSL Certificate at this time.
You can read more on how to detect and fix an inactive DNS Zone (which is what happens when you are using a Netlify DNS configuration but not the Netlify name severs):
This guide will lead you through how to detect an inactive DNS Zone, and how to fix the issue.
TLDR, you’ll only want to configure either External DNS or Netlify DNS, not both at the same time.