Note: this discussion was Google-translated.
How to configure wildcard HTTPS *.subdomain.domain.com to Heroku?
Heroku ACM does not support LE wildcard certs, so if you want to use Heroku, you will have to apply the cert yourself, for example as a cronjob. As such, short scripts can be found on Google, so no problem for Mr. manual labor. But LE wildcart cert requires DNS Challenge, so you need API Access for your DNS provider. If you have static thingery, swap it with Netlify, with DNS there, and ask support to activate support for the wildcard subdomain. Success with the pro plan.
The third option is to use some Heroku SSL plugin to get wildcard ssl (instead of Heroku's own ACM). In those, I think the cheapest was something like 75 a month.