iOS 12.1.3 (build 16D40) is an official Apple over-the-air update for the iPhone XR, released on 2019-01-22T18:15:09Z. The update package is 385.11 MB. This is a delta (partial) update that requires 12.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b5ce0108145c2822d6c9dc58d439029d920ce42c.zip.