I keep finding solutions how to do it with moshi using:

val typed = Types.newParameterizedType(Envelope::class.java, type)

however I'd like to avoid pulling moshi in just to be able to work around the reflection definition

this channel is for kotlinx.serialization .. not quite retrofit.. in ktx-serialization your envelope class would be fine as is.. aside from missing the annotation.. and use it as

Envelope.serializer(ResponseClass.serializer())

Yeah I know Its not retrofit related question. The key problem is how to define this:

val response : Envelope<type> = json.decodeFromString(...)

I have no idea how to properly tell kotlinx.serialization about the type i get dynamically

when there is a generic, the serializer function takes a parameter for the serializer of each generic type parameter:

Envelope.serializer(type.serializer())

Envelope.serializer(type.javaClass.kotlin.serializer())

that one worked. Thanks a ton!