Unfortunately on iOS it will only return dummy values for the mac address:
Apple introduced the restriction in iOS 7 from memory.
Android should return the correct address, however some devices may not. Seems some manufacturers deny accessing this information. You may require some additional permissions in your manifest, particularly
Honestly we highly recommend not attempting to use the mac address on mobile. It's not a reliable identifier, you are better off using the vendor unique id (Application ANE) or the advertising id (IDFA or Adverts ANEs), depending on your needs.