Beyond just moderating what gets posted, Apple requires the app itself to ship with a working content filter, an in-app way to report objectionable content or users, and the ability to block another user — in place before launch, not added after complaints.
Very commonly caught in social, chat, or dating apps that launch with a "report" button that doesn't actually route anywhere, or without any block feature at all.
"Your app includes user-generated content but does not have the required content moderation tools in place, per guideline 1.2. Apps with UGC must include a way to filter objectionable content, report it, and block abusive users."