validation.scala

        val validTask  = (json \ "taskId").asOpt[String] match {
          case Some(taskId) if taskId.contains("UNUSED_") => new Exception("Ignoring %s, its unused event and not supposed to be billed.").fail[String]
          case Some(taskId) if !taskId.isEmpty => taskId.success[Throwable]
          case _ => new Exception("taskId does not exist").fail[String]
        }