How to read "com.apple.configuration.managed" Using MDM To Configure An Enterprise App Via UserDefaults - Swift 3 or 4

Question

let serverConfig = UserDefaults.standard.dictionary(forKey: "com.apple.configuration.managed") print("serverConfig count:
\(String(describing: serverConfig?.count))")

Above code always returning nil for iOS 11 and above. but same code is working for me on iOS 9,10.

I have checked this ref link code but somehow it's not working fine for me. I don't know what I'm doing wrong.