Issue
Your application uses a wildcard domain and that prevents you from using our Automated Certificate Management (ACM) feature. You would like us to support it and wonder why it's not possible.
Resolution
Automated Certificate Management (ACM) only supports wildcard domains for applications in the Common Runtime. This means Private Spaces apps using ACM can't have wildcard domains, this is mentioned in the known limitations section of our Dev Center article.
If you want to automatically renew a wildcard certificate on a Private Space app, Heroku add-ons such as SSL FastTrack or ExpeditedSSL might serve your use case.