Description

The digital-payment-credentials README instructs users to set GOOGLE_API_KEY in local.properties, but app/build.gradle.kts reads GEMINI_API_KEY. This results in the Android app getting an empty API key, causing a 403 PERMISSION_DENIED error when calling the Gemini API.

Steps to reproduce

1. Follow the README at samples/android/scenarios/digital-payment-credentials/README.md
2. Set GOOGLE_API_KEY=your_key in local.properties as instructed
3. Build and run the app
4. Send a message in the chat

Expected behavior

The app should call the Gemini API successfully.

Actual behavior

403 PERMISSION_DENIED: "Method doesn't allow unregistered callers (callers without established identity)."

Root cause

app/build.gradle.kts line 32 reads GEMINI_API_KEY from local.properties, but the README tells users to set GOOGLE_API_KEY.