Your CNAME entry should be to the SSL endpoint NOT to your Heroku application.
www.gewerbeverzeichnis-rj.ch CNAME toyama-4181.herokussl.com
That will stop the SSL error message rather than trying to use the wildcard *.herokuapp.com certificate that it is using when you CNAME to .herokuapp.com
This particular setup step is at https://devcenter.heroku.com/articles/ssl-endpoint#dns-and-domain-configuration