To redistribute code written with Mono for Unreal Engine, you must have a commercial license to the Mono runtime. These licenses are available from Xamarin for

To redistribute code written with Mono for Unreal Engine, you must have a commercial license to the Mono runtime. These licenses are available from Xamarin for Mac, Android and iOS online, and you can request Windows licenses through support. https://mono-ue.github.io/about.html https://mono-ue.github.io/about.html If you want to code in C# it is the primary language for Unity, and a commercial third party unsupported add on for UE4.