Troubleshooting
the parameter pkg_name and sign_key are required / "The application is not approved"
The package name or hash key registered on the Zalo Developer Portal does not match the running build. Compare them with getApplicationHashKey(). Builds installed from Google Play are signed by Google: see Play App Signing.
"Application is not registered for this request"
Request the permissions your app needs on the Zalo Developer Portal (see Create a Zalo app).
Login never returns on iOS
Make sure AppDelegate forwards application(_:open:options:) to ZDKApplicationDelegate before other handlers, and that the zalo-<appId> URL type exists. See the iOS setup.
NOT_CONFIGURED
The Zalo App ID is missing: the com.zing.zalo.zalosdk.appID meta-data on Android (setup), or ZaloAppID in Info.plist on iOS (setup).
Gradle: Could not find me.zalo:sdk-core
Your build ignores the repositories added by libraries, usually because settings.gradle sets dependencyResolutionManagement. Add the Zalo Maven repository there.