Moshi custom serializer on interface type implemented by enums

Question

I am trying to implement a custom Moshi adapter, only for serialization, that serializes the enum constant instead of the enum type itself.

interface ApiType {
  val id: Int
}

enum class Gender: ApiType {
  MALE {
    override val id: Int = 1
  },
  FEMALE {
    override val id: Int = 2
  }
}

And the adapter:

class ApiTypeAdapter {
  @ToJson
  fun toJson(apiType: ApiType): Int {
    return apiType.id
  }
}

On the adapter, if I replace the interface type ApiType with Gender it works as expected. The thing is that i am gonna have many types that should be serialized as such and I want to generalize the adapter.

How can I make the adapter work on all the enums that implement the ApiType?