(if errors persist) Settings > Apps > Google Play Services > Storage > Clear Cache (do NOT clear data unless necessary).
Because you are installing an APK file manually (outside of the Play Store), Android 8.1.0 requires you to give specific permission to your browser or file manager. Google Play Services Apk Download For Android 8.1.0
You're looking for a review of Google Play Services APK download for Android 8.1.0. (if errors persist) Settings > Apps > Google
