Package is not found in the following primary source

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.

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