What's the best way to get an APK for app update?

I'm creating an App Updater for my android App and since the app can't go on the Play Store I need to get my APK from somewhere else. I'm already getting a JSON through an HTTP Request from my server that contains the version of the latest app. Is there a way to send the APK within that JSON to be downloaded after? If so I would appreciate some insight into how that is done. If there is a bette way I'm all ears too!