There is no question that the future of parsing in Kotlin will be with kotlinx.serialization. It is part of Kotlin libraries. Version kotlinx.serialization 1.0 is finally released

https://github.com/Kotlin/kotlinx.serialization

Copyimport kotlinx.serialization.*
import kotlinx.serialization.json.Json

@Serializable
data class MyModel(val a: Int, @Optional val b: String = "42")

fun main(args: Array<String>) {

    // serializing objects
    val jsonData = Json.encodeToString(MyModel.serializer(), MyModel(42))
    println(jsonData) // {"a": 42, "b": "42"}
    
    // serializing lists
    val jsonList = Json.encodeToString(MyModel.serializer().list, listOf(MyModel(42)))
    println(jsonList) // [{"a": 42, "b": "42"}]

    // parsing data back
    val obj = Json.decodeFromString(MyModel.serializer(), """{"a":42}""")
    println(obj) // MyModel(a=42, b="42")
}

I can see that you want to serialize the ArrayList<UserPatient>. You can do it easily with Gson.

Example:

val response = AccountInfoResponse(/* Here goes the objects that is needed to create instance of this class */)

val jsonString = Gson().toJson(response.userpatients)

Output:

{"userpatients":[{"sex":"male","date of birth":"2010-01-03","image":"","clinics":[1],"primary_provider":[{"clinic":1,"patient":1,"providers":1}],"role":"patient","last name":"John","address":"300 east main st.  San Jose, Ca 95014","first name":"John","username":"John","email":"[email protected]","mobile":"+88083918427"}],"userpatients":[{"sex":"female","date of birth":"2000-01-01","address":"fawal st1","patientID":1,"first name":"john","clinicName":"light house peds","clinicID":1,"mobile":"8056688042","last name":"john"}]}