Apple rejects most first submissions for the same handful of reasons, and each one has a known fix. This is one page per guideline: Apple's own text, what the rejection message says, the fix in order, and the reply to send when the reviewer is wrong.
The verdict lands in the Resolution Center in App Store Connect and in an email, naming the guideline by number. Reply there. If the fix is in your Rails app, deploy it and reply; the app loads its pages from your site, so there is no new build. If the fix is in the listing, change it and reply. A new build is only needed when something in the binary changes, like the icon or a permission string. Most cycles run under 24 hours, so plan for one or two and treat each reply as the whole case.
If the reason is not on this list, the App Store review guide covers the rest of the review, and the submission guide covers the fields the reviewer reads.
From Joe: TODO one line on the rejection that comes up most, and the reply that ends it.
With the launch review, send the rejection to Joe from your dashboard. He reads Apple's message and replies within two business days with exactly what to change, or the reply to send when the reviewer is wrong.
See the launch review