Hello!
Here are the recommended steps to downloading the latest Newtonsoft.Json package for Unity projects. Prior to following the steps mentioned below, I would recommend removing the previously added DLL of the package and reopening the project as to avoid any errors.
- Open the Package Manager window in your Unity project.
- Click the plus icon on click "Add package from git URL"
- Paste this in the URL field and then press Add:
com.unity.nuget.newtonsoft-json@3.0