SDK Version Issue - This app was built with the iOS 12.0 SDK. Starting March 2019, all iOS apps submitted to the App Store must be built with the iOS 12.1 SDK or later, included in Xcode 10.1 or later.
Because I'm using Expo, how to Update iOS SDK Version in Expo?
There are two different scenarios:
Building on Expo Server
A quick test:
expo-cli build:iosThis gives the value 10A255, which actually indeed means Xcode 10.0 released on 17 Sep 2018.
As mentioned by Jeaf Gilbert in the comments, Expo is aware of this:
thanks for reporting! We're aware of this warning and we promise the issue will be resolved before March 2019
see here: https://github.com/expo/expo-cli/issues/264
Ejected to ExpoKit
If ejected to ExpoKit then Expo is using the SDK of the installed Xcode version, because the building is managed locally.
In this case just install the newest Xcode version. This also includes the newest SDK.