Add the Mint Mediation Unity software package to your project by following the steps below:
Download Mint Mediation Unity Plugin and import it in the .unitypackage file.
Navigate to Assets -> Import Package -> Custom Package.
Select the Mint MediationUnityPlugin.unitypackage file.
Import all files, and ensure to avoid the confliction with files. (Double click the decompressed file. Different files will be automatically filled as shown below.)