Deserializing json with PolymorphicJsonAdapterFactory and Retrofit

[niclashalvorsen]

I have read about every blog and documentation there is about Moshi's PolymorphicJsonAdapterFactory but i cannot make it work for some reason.

Retrofit API & DTO's:

interface Api {
    @GET
    suspend fun getPayment(): Payment
}     

sealed class Payment()

data class Domestic(amount : Double) : Payment()
data class International(amount : Double): Payment()
class Unknown(): Payment()

Moshi & Retrofit setup:

val adapter = PolymorphicJsonAdapterFactory.of(Payment::class.java, "paymentType")
    .withSubtype(International::class.java, "INTERNATIONAL")
    .withSubtype(Domestic::class.java, "DOMESTIC")
    .withDefaultValue(Unknown())

val moshi = Moshi.Builder()
    .add(adapter)
    .add(KotlinJsonAdapterFactory())
    .build()
                
val retrofit = Retrofit.Builder()
    ..... 
     .addConverterFactory(MoshiConverterFactory.create(moshi))
    .build()
    .create(Api::class.java)

My dependencies:

implementation "com.squareup.retrofit2:retrofit:2.9.0"
implementation "com.squareup.retrofit2:converter-moshi:2.9.0"
implementation "com.squareup.moshi:moshi:1.14.0"
implementation "com.squareup.moshi:moshi-kotlin:1.14.0"
implementation "com.squareup.moshi:moshi-adapters:1.14.0"

I have tried making the super class open, sealed class and interface.
Sealed:

Caused by: java.lang.IllegalArgumentException: Cannot reflectively serialize sealed class Payment. Please register an adapter.
    at com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory.create(KotlinJsonAdapter.kt:224)

Interface:

Caused by: java.lang.RuntimeException: Failed to find the generated JsonAdapter class for interface "Payment"
    at com.squareup.moshi.internal.Util.generatedAdapter(Util.java:590)

Open:
Dosent crash, but i'm just getting a Payment object without a parent.

I have tried to add @JsonClass(generateAdapter = true) on the data classes (and the parent) but it makes no difference.

I have also tried older versions of Moshi, but dosent seem to work for me there either.

What am i missing here?