Package is not found in the following primary source

I waited another 5 minutes and the problem went away. Maybe the version shows before the publishing is complete.

You have to check your package source I think the default is

Microsoft Visual Studio Offline Packages 

So, you can change that to "All".

After 4 hours struggle I found solution here https://www.grapecity.com/componentone/docs/uwp/online-getting-started/config-nugetpackage.html

Tools > Options > NuGet Package Manager > Package Sources. > Click add button and add following one by one...

nuget.org https://www.nuget.org/api/v2/

GrapeCity http://nuget.grapecity.com/nuget

This is caused by caching. If you don't want to wait like the above answer suggested, just clear Nuget caches by going to Tools -> Options -> Nuget -> General and click on the "Clear All Nuget Cache(s)" button.