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Limited Facebook functionality is implemented in the Unity Editor and behavior may not be the same as when used on a native platform like iOS, Android, or Web. It is best to test Facebook functionality on a real device.
Since many of the social features provided in the Facebook SDK are part of native Facebook's app for each platform, they cannot run on a simulator. Use a physical device to test the native Facebook functionality.
To use the Facebook SDK for Unity on Android, you need to tell Facebook about the key that you use to sign your apps.
This is a key hash which is a SHA-1 hash of the key used to sign your app. Usually there will be at least two different keys used: one for development and debug, and one for release. so be sure to add both values in your app's Settings page.
For more information, see Getting Started Android SDK, Create a Development Key Hash.