That’s the easy solution. A more complicated solution is to do Setting up Let’s Encrypt with Multiple Domains to add another domain to the let’s encrypt request, which will sneak you past the rate limit you hit (since asking for forum.x.com and silly.x.com is a different request. But it requires some careful changes to your app.yml and your DNS config, which is what got you into the trouble that you’re in. If you can wait a week, you can just wait and just rebuild when the time is up.