iOS 11.3.1 (build 15E302) is an official Apple over-the-air update for the iPhone 6+, released on 2018-04-24T17:10:15Z. The update package is 740.76 MB. This is a delta (partial) update that requires 11.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7428ff56d63c2f8d62b09bbf8fa31e47a5bfc277.zip.