You can get the Application Id (App Identifier) for your mobile app in the same place where you generate the mobile app package.

In OutSystems 11:

1. Open Service Studio and select your Mobile App module.
2. Go to Module → Generate Mobile App… (or right‑click the module and choose Generate Mobile App).
3. In the Generate Mobile App window, you’ll see the App Identifier field (sometimes also shown as the Package Id / Bundle Id depending on platform).
4. Use that value (in lowercase) as the <scheme> in your deeplink:
   outsystemsapp://<appidentifier>/<module>/<screen>

The deeplink syntax is described here: :<scheme>://<module>/<screen> where <scheme> is your App identifier in lowercase. How to define Mobile App deep links

So:

• App Identifier shown in Generate Mobile App = Application Id for deeplinks (convert to lowercase when using in the URL).