'MyMacros.ExposeMacro' is not a valid macro implementation type in library plugin

I have a simple macro to replace @main on wasm that I compiled into a .dylib and used with -load-plugin-library build/libMyMacros.dylib. I am using Embedded Swift and targeting wasm32

What does the error mean?

Ok I see, it has to be an executable not dylib. not very clear from the help option, I don't understand why there's two of them