When attempting to publish the website on a custom domain, the status should show an error with the following divs containing instructions. While I can try and access the using developer tools, it would be cool if the status message had the option to be folded down to a single row (or be expanded) as your documentation suggests it usually just says "Error" or something.
This is literally my entire screen height.
I opened the site builder in the Web app, clicked publish in the top right corner. I added my domain and it threw this error. I have a subscription (Pro).