koltin serialization polymorphizm. "type" field in json

serializationtype.kt

import kotlinx.serialization.DeserializationStrategy
import kotlinx.serialization.Serializable
import kotlinx.serialization.encodeToString
import kotlinx.serialization.json.*
import kotlinx.serialization.SerialName

@Serializable
@JsonClassDiscriminator("mytype")
sealed class ContentRequest

@Serializable
data class MessageRequest (
    val type : String = "text",
    val text : String
) : ContentRequest()

@Serializable
@SerialName("another type")
data class AnotherRequest (
    val type : String = "very important text",
    val text : String
) : ContentRequest()

fun main() {
    val messageRequest = MessageRequest("one","two") 
    val contentRequest: ContentRequest = MessageRequest("one","two")
    val anotherRequest: ContentRequest = AnotherRequest("one","two")

    println(Json.encodeToString(messageRequest)) // {"type":"one","text":"two"}
    println(Json.encodeToString(contentRequest)) // {"mytype":"MessageRequest","type":"one","text":"two"}
    println(Json.encodeToString(anotherRequest)) // {"mytype":"another type","type":"one","text":"two"}

}

https://pl.kotl.in/ryUXNfOsv