iOS 12.1.3 (build 16D39) is an official Apple over-the-air update for the iPhone 6s+, released on 2019-01-22T18:11:37Z. The update package is 1.35 GB. This is a delta (partial) update that requires 11.3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 49e190ce5b97361cceb8a7f8ef4fbb5ca948794a.zip.