1

Set Application Identifier Prefix and Bundle Identifier

As explained in iOS: Overview, the Apple-App-Site-Association (AASA) file plays a crucial role in using passkeys in your Flutter app.
  1. On the developer panel, Go to Settings → Native apps
  2. Click on Add new.
  3. Insert your Application Identifier Prefix and your Bundle Identifier.
    Use your team ID as the Application Identifier Prefix. You can find it at https://developer.apple.com/account under “Membership”.
    Team ID Apple
  4. Submit the new iOS App
    You can view your changes live through the association file link found in Settings → Native apps
2

Update Runner.entitlements

To link your Flutter app with the associated domain:
  1. Open ios/Runner/Runner.entitlements
  2. Add the following association domain (Change with your RPID):
<key>com.apple.developer.associated-domains</key>
<array>
    <string>webcredentials:<Your RPID>?mode=developer</string>
</array>
As mentioned before, we want to bypass the Apple-App-Site-Association (AASA) file caching in development, so we need to specify the ?mode=developer here.
Do not use the ?mode=developer parameter in your production release. This parameter is intended for development purposes only. Using it in production will prevent iOS from properly detecting your AASA file, which will break passkey functionality in your released app.