iOS 12.1.3 (build 16D39) is an official Apple over-the-air update for the iPhone 6+, released on 2019-01-22T18:09:58Z. The update package is 1.86 GB. This is a delta (partial) update that requires 10.3.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 4764cbea03181a5fb2d50a692eeb61c4c51d5309.zip.