With the update on 2-February-2022, we have dramatically simplified this process. It now works just like any other hosting and we completely handle the SSL certification creation automatically.
All you have to do is log into your domain registrar and point your domain name to this IP address: 52.21.211.236
You can use either a root domain (mynewsite.com) or a subdomain (blog.mynewsite.com). Since we are now using a IP address, in both cases you just provide a single "A record" for the domain of your choice.
After setting up your registrar, open the blog Credential in ResultFlow, enter the domain name you just modified at your registrar, and press "Update" on the Credential.
If it doesn't work immediately, give your registrar DNS a few minutes to propagate, and then open and press update on your Credential again.
Note that the vanity domain field, use only the domain name, no http or https in front and no trailing '/'.