Why Apple has rejected my app?
Apple rejects all the apps that don’t meet its guidelines. Apple reviews all the submitted/resubmitted app, evaluates it, and once an app meets all their guidelines then only it get published on iTunes. In case, your app doesn’t meet any of their guidelines then it will be rejected and Apple will send you an email to notify you regarding rejection of the app. You can know why Apple has rejected your app by login into your iTunes connect account.
You can check Apple Guidelines here: https://developer.apple.com/app-store/review/guidelines/
If you are unable to know the reason(s) for rejection or are unable to get it fixed, then please contact Appy Pie support team, they will help you resolve rejection issue.