licence fees on android because of mono (c#). Is this correct?

On every platform i have to pay licence fees to Xamarin, except on Windows!?

Is this true?

Or is this only for guys who wants to implement Mono in his APIs like MonoGame do. So the MonoGame users doesnt have to pay anything.

When i use Unity on Android i doesnt have to pay those fees. Or do I?

Can someone tell me more about it?

Mono is collectively the compiler, runtime, framework assemblies and other tools that allow development in C#, F# and other .NET technologies on non-Windows platforms (Mono does support Windows as well, but it’s not widely used). Xamarin own Mono, and require licenses for it to be used to build apps on iOS, Android, OS X and PS4. Mono is free to use and build apps with on Linux and Windows.

MonoGame is a library that is built with a .NET compiler and framework, whether that compiler and framework come from Microsoft or Xamarin. There are no Mono APIs implemented in MonoGame, and there is no Xamarin license exemption from using MonoGame.

Unity paid their license fees many years ago for iOS and Android. This allows them to distribute a heavily customized Mono compiler and runtime with Unity, but it also means that the compiler and runtime that they distribute is now very out of date compared with the latest from Xamarin.

To build, debug and distribute apps built with Xamarin on iOS, Android, OS X and PS4, you will need a licensed copy of Xamarin Studio.