Guideline 4.3
Duplicate app / Spam
App provides the same features and user experience as other apps already submitted by you or another developer. This is the #1 reason for App Store rejections. Apple aggressively targets apps that are clones, reskins, or near-duplicates of existing apps.
26 cases reported · ~26 days to resolve · 57% appeal success
Apple's rejection message
Guideline 4.3 - Design - Spam: Your app duplicates the content and functionality of other apps submitted by you or another developer to the App Store, which is considered a form of spam.