iOS 12.1.3 (build 16D5039a) is an official Apple over-the-air update for the iPhone 8 Plus (GSM), released on 2019-01-10T18:08:57Z. The update package is 296.33 MB. This is a delta (partial) update that requires 12.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c186f735790dbe1f93c134df37fc50ffd13edd3a.zip.