Apple provides different types of app builds, depending on your use case.
In order to create any type of build, the build settings for your app on the platform must contain the relevant Bundle Identifier. For more details about build settings, please check this article.
In order to build an iOS app with the macOS app, you need to have an app in Production Mode on the Twixl platform.
1. Ad Hoc build
iOS Developers enrolled in the standard iOS Developer program have the opportunity to distribute their application outside of the App Store on up to 100 devices. Use the Ad Hoc Bundle ID in the build setting of your app to create a build of your app to distribute internally. Make sure you define the necessary devices (at least one!) that can be used in the Apple Developer portal first, as described here.
2. Enterprise build
iOS Developers enrolled in the iOS Developer Enterprise program have the opportunity to distribute their application outside of the App Store and without the 100 devices limit. Use the Enterprise Bundle ID in the build setting to distribute a build of your app internally.
3. App Store build
Use the "App Store" Bundle ID in the build setting to create a build that you will be submitting to the App Store (or to TestFlight first).