Cannot receive a user's email using Sign in with Apple

Recently I have developed Sign in with Apple feature in my iOS app. It was almost similar like Facebook login.
By the way I faced an issue that I couldn't get a user's email after the initial sign up. Then I found a link that Apple engineer answered.

So if you are testing Sign in with Apple feature go to iOS Settings and remove the previous sign in permission. Then you might save the user information such as the email address into your database.

Another issue that I found in Sign in with Apple

Apple said that they generated a fake email address that redirects an email to a user’s iCloud email address. By the way this issue could cause a duplicated signup if a user uses the email address in other service such as Facebook. So Apple’s approach is like pushing your app to use the only Sign in with Apple feature. But according to Apple’s guideline you have to provide “Sign in with Apple” if you use other service such as Facebook login.