I found out what is your issue.
Okay so the name of your project is “BoxMobile”
Unreal engine always creates a class name ProjectName+Target. in your case it is BoxMobileTarget. it is kept in the source directory . under ProjectName.Target.cs and it takes care compilation specific features of your project. it is a C# file but still, you can’t have a class with the same name.
Another class that will be created automatically is ProjectName+Editor+Target which in your case is “BoxMobileEditorTarget”
In short, you need to use another name