iOS 12.1.3 (build 16D5037a) is an official Apple over-the-air update for the iPhone 8 Plus (GSM), released on 2019-01-07T18:07:09Z. The update package is 297.24 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: f3cc2c1ef6280f601b970fd8c26fedcebace0025.zip.