Here is code from Auth guard:

  val sessionToken = call.request.cookies.get("session_token")
  if (sessionToken == null) throw HttpException(HttpStatusCode.Unauthorized, "Unauthorized", "User is not authorized, please login")

HttpException:

class HttpException (
  val statusCode: HttpStatusCode,
  val errorType: String,
  val errorDetail: String,

  ) : Exception("HttpException")

In App.kt :

  install(ContentNegotiation) { json() }
  .....
  @Serializable
  data class ErrResponseBody (val errorType: String, val errorDetail: String)

  install(StatusPages) {
    exception<Throwable> { call, cause ->
      when(cause) {

        // http error
        is HttpException -> {
          val responseBody = ErrResponseBody(cause.errorType, cause.errorDetail)
          println(responseBody)
     
          //call.respond(cause.statusCode, "AAAAAAAAAAAAAAA") // this one work for some reason!
          call.respond(cause.statusCode, responseBody)
        }

        // 500
        else -> {
          val responseBody = ErrResponseBody("Internal server error", "")
          call.respond(HttpStatusCode.InternalServerError, responseBody)
        }

      }
    }
  }

I’ve made sure execution happens till error handler
So, here is the problem:
Serialization there not works, and call.response(T) not works

With returning ErrResponseBody (serialization required)

enter image description here

Without (with “AAAAAAAAA” instead of T)

enter image description here