I have this error. When using Retrofit2

Caused by: kotlinx.serialization.SerializationException: Serializer for class 'Result' is not found.
    Mark the class as @Serializable or provide the serializer explicitly.
        at kotlinx.serialization.internal.PlatformKt.serializerNotRegistered(Platform.kt:32)
        at kotlinx.serialization.SerializersKt__SerializersJvmKt.serializer(SerializersJvm.kt:60)
        at kotlinx.serialization.SerializersKt.serializer(Unknown Source:1)
        at com.jakewharton.retrofit2.converter.kotlinx.serialization.Serializer.serializer(Serializer.kt:24)
        at com.jakewharton.retrofit2.converter.kotlinx.serialization.Factory.responseBodyConverter(Factory.kt:28)
        at retrofit2.Retrofit.nextResponseBodyConverter(Retrofit.java:362)
        at retrofit2.Retrofit.responseBodyConverter(Retrofit.java:345)
        at retrofit2.HttpServiceMethod.createResponseConverter(HttpServiceMethod.java:124)
        	... 90 more

Is there any problem?...

val serializationJson = Json {
            useAlternativeNames = true
            isLenient = true
            ignoreUnknownKeys = true
        }

        return Retrofit.Builder()
            .baseUrl(baseUrl)
            .client(client.build())
            .addCallAdapterFactory(CoroutineCallAdapterFactory())
            .addConverterFactory(ScalarsConverterFactory.create())
            .addConverterFactory(serializationJson.asConverterFactory("application/json".toMediaType()))
            .build()

I think the issue is not in the setup but how you use the serializer. How did you configure the

Result

class? Did you add the Annotation as spotted in the error report?

yes. Here's the data class.

import kotlinx.serialization.Serializable

@Serializable
data class ManagerLoginResponseBody(
    val id: Int,
    val kiosk: String, // will be removed
    val created: String? = null,
    val modified: String? = null,
    val name: String,
    val mobile: String,
    val role: String,
    val branch: BranchModel,
    val token: String
)

But that’s not the

Result

class Form the error.

the Result class is from kotlin library

If you use it, you’ll need to create a serializer for it.

isn't this part?

.addConverterFactory(serializationJson.asConverterFactory("application/json".toMediaType()))

No

How can I create a serializer ??

Please check the documentation of the Kotlinx serializer plug-in. There are plenty of examples how to create a serializer.