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"

kapt("com.squareup.moshi:moshi-kotlin-codegen: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?

[niclashalvorsen]

BTW this works when creating an adapter, but not when setting it as a part of Retrofit with addConverterFactory()

moshi.adapter(Payment::class.java).fromJson("....")

[laaptu]

Any solution on this issue. I am also facing the same and haven't been able to find any solution. The debugger shows that CustomAdapter is attached to the Moshi but it never gets called to serialize the sealed class.
As pointed out by @niclashalvorsen , it works only when creating a standalone adapter with the sealed class name but never works with Retrofit with addConverterFactory.