Could not load file or assembly 'Facebook.Unity.Android' or one of its dependencies.

Questions & Answers
1

Using gradle to build apk, Unity 5.5.
Get errors of Facebook sdk as below:

Non-fatal Exception: java.lang.Exception: FileNotFoundException :  Could not load file or assembly 'Facebook.Unity.Android' or one of its dependencies. The system cannot find the file specified.
       at System.AppDomain.Load(System.AppDomain)
       at System.AppDomain.Load(System.AppDomain)
       at System.AppDomain:Load(System)
       at System.Reflection.Assembly.Load(System.Reflection.Assembly)
       at Facebook.Unity.Mobile.Android.AndroidFacebook.GetAndroidWrapper(Facebook.Unity.Mobile.Android.AndroidFacebook)
       at Facebook.Unity.Mobile.Android.AndroidFacebook..ctor(Facebook.Unity.Mobile.Android.AndroidFacebook.)
       at Facebook.Unity.Mobile.Android.AndroidFacebookLoader.get_FBGameObject(Facebook.Unity.Mobile.Android.AndroidFacebookLoader)
       at Facebook.Unity.FB+CompiledFacebookLoader.Start(Facebook.Unity.FB+CompiledFacebookLoader)

Could anyone help me locate where the problem is? or just give some suggestions on solution.

2

Happened to me as well.

I select the file
Assets/FacebookSDK/Plugins/Android/Facebook.Unity.Android.dll

In the Inspector > Select platforms for plugin.
Check “Android” , Apply.

Then it is solved.