NuGet Package Manager Console returns InvalidOperation when trying to install the ZXing.Net library

I am trying to install the ZXing.Net library to VisualStudio 2019 to use in Unity but entering the command in the console returns a category of InvalidOperation

I just copy pasted the code right our of ZXing.Net in nuget.org but it returned this error:

PM> Install-Package ZXing.Net -Version 0.16.5

Install-Package : The current environment doesn't have a solution open.
At line:1 char:16
+ Install-Package <<<<  ZXing.Net -Version 0.16.5
    + CategoryInfo          : InvalidOperation: (:) [Install-Package], InvalidOperationException
    + FullyQualifiedErrorId : NuGetNoActiveSolution,NuGet.PackageManagement.PowerShellCmdlets.InstallPackageCommand