I have upgraded my project to 2019.4.28f1 when ever I install new version or verified version from package manager it gives the following error.
Library\PackageCache\com.unity.purchasing@4.0.0\Runtime\WinRTStub\Factory.cs(15,23): error CS0433: The type ‘IWindowsIAP’ exists in both ‘UnityEngine.Purchasing.WinRTCore, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null’ and 'winrt, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null,> Blockquote
Library\PackageCache\com.unity.purchasing@4.0.0\Runtime\WinRTStub\Factory.cs(15,23): error CS0433: The type ‘IWindowsIAP’ exists in both ‘UnityEngine.Purchasing.WinRTCore, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null’ and 'winrt, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null