
We recently transitioned one of our core apps to [EAS Build](https://docs.expo.dev/build/introduction/) as part of moving to Expo 48.

Right out of the gate, the app ran perfectly in Expo Go.  We pushed a build, and in TestFlight, the app instantly crashed.

So, what can you do when that happens?  Here are some quick tips.

## Expo prebuild & XCode build

This can surface quite a few build time errors.  The first thing you do is run...

```bash
$ npx expo prebuild --platform ios
```

Similar to ejecting, this creates an `ios` folder in your project with all of your XCode artifacts and pods.  However, we're not gonna keep this permanently.  We're just going to load up XCode with...

```bash
$ xed ios
```

Run the project using the **play** button in XCode, and see if you have any build errors.

![XCode no build errors](/images/xcode-no-build-errors.png 'image_tooltip')

This will also run the built package in the simulator of your choice, which is really helpful for debugging app errors in your build.

For example, we had a bug in TestFlight where our `react-native-maps` view would not render.  Everything seemed to work in Expo Go, but by building through XCode we were able to discover there were errors to fix.

![React Native Maps Error](/images/ios-maps-errors.png 'image_tooltip')

And after using the XCode build to find and fix the error (this one happened to be a missing API key), the app works!

![React Native Maps Clean](/images/ios-maps-clean.png 'image_tooltip')

Once you've fixed the issues, you can delete the `ios` directory to ensure you stay in managed workflow...

```bash
$ rm -rf ios
```

... and easily resubmit your apps with the EAS Build service in one simple command:

```bash
$ eas build --auto-submit
```

If your [credentials are set up](https://docs.expo.dev/deploy/submit-to-app-stores/), everything will automatically go out to TestFlight and the Play Store!

Happy hacking! 😎



Is your Expo managed iOS app crashing in production?  Here is a tip I've used to identify troublesome bugs that only happen in production.