Ravindra Sendhav “If you create an instance of a Realm, you can use it only on the same thread. If you want to use the same Realm on another thread, you have to create a new Realm instance on that other thread”

The best practice is to parse response on swift model first and when you get the parsed swift model in main thread , you can create new thread with new realm instance and map swift model into realm model. Hope it will help