In case you use an older version of Unity you need to add the Newtonsoft Json package. You can install it by pasting following into your manifest.json file:
"com.unity.nuget.newtonsoft-json": "3.2.1",
In the new Unity versions the Newtonsoft Json is build in to Unity. No need to install the package.
Dependencies Installation:
Git package repository link. The easiest way to add the READYgg SDK into your project is to use PLAY package distribution. You need simply put the package git repository links into manifest.json file. See instructions below.
Troubleshooting : if you have error messages in Unity saying that it cannot find the git repository, make sure you have Git installed on your machine. Unity Hub needs it to import packages from Github.
Steps:
Open [project_dir]/Packages/manifest.json file in your favorite text editor
