Setting up a Xamarin.Android project for code signing
When App Center builds a Xamarin.Android application with a debug build type, a keystore associated with a developer is not required. These builds will be automatically code signed with a debug key. For a release build that will be deployed, App Center will require a keystore to be uploaded.
Generating a keystore
If you do not currently have a keystore, you can generate one using instructions specific for the OS and IDE of your choice.
1. In Windows
You can use the instructions for different versions of Visual Studio to generate a keystore. Or, if you want to use the command line, check: 2. Android: Generate a Private Certificate in Cross Platform Development Documentation
2. In macOS
Setting up Code Signing
App Center currently supports signing only with the uploaded keystore files and credentials. Keystore files have the extension .keystore or .jks. After toggling on "Sign builds" in the branch configuration, either click the Keystore file box to choose or drag your keystore file into it. Enter the keystore password, the key alias, and the key password to allow App Center to complete the signing of your APK.