I am getting Email and FullName as nil values when I am trying to SignIn with Apple

Did you aware of defining request scopes while you were performing request?

Your code should be some how similar to this:

        let appleIDProvider = ASAuthorizationAppleIDProvider()
        let request = appleIDProvider.createRequest()
        request.requestedScopes = [.fullName, .email]
        let authorizationController = ASAuthorizationController(authorizationRequests: [request])
        authorizationController.delegate = self
        authorizationController.performRequests()

And when you receive the response, after converting it to ASAuthorizationAppleIDCredential, You can see fullname and email address by printing them out :

func authorizationController(controller: ASAuthorizationController,
                             didCompleteWithAuthorization authorization: ASAuthorization) {
    switch authorization.credential {
    case let appleIDCredential as ASAuthorizationAppleIDCredential:

        debugPrint(appleIDCredential.email) //prints either 'email' or 'proxied email'
        debugPrint(appleIDCredential.fullName) //prints name 'object'

    default:
        break
    }
}

Edit: If problem persists, go to settings -> profile -> password and security -> apps using your apple id find your app and revoke its access and try again!

1. If the user select hide my email then the value of email will nil. No way to get the email.
2. For the first time authentication, you can get the user fullName. But in second-time authentication, the value of fullName will be nil.

For more you can check this: ASAuthorizationAppleIDRequest with name and mail scope returns nil values