iPadOS 12.4 (build 16G5077a) is an official Apple over-the-air update for the iPad Air 2 (WiFi), released on 2019-07-16T17:39:04Z. The update package is 281 MB. This is a delta (partial) update that requires 12.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7b1f28d07dd2302e6fcb2d8de91c7d13ca89b93f.zip.