You are attempting to install an older version of the Play Store over a newer version already running on your phone. Android does not allow downgrades via APK. Check your current version in Settings > Apps > Google Play Store and ensure the APK you downloaded has a higher version number.
If you want, I can:
: Widely considered one of the safest sources. It hosts numerous versions, including the Google Play Store 50.8.18 google play store apk for android 810 link
: Use the links above to download the APK. Once finished, tap the notification or find the file in your Complete Setup
For Android 8.1.0, you generally want the most recent "universal" or "arm64-v8a" variant of the Play Store APK. You are attempting to install an older version
Go to . Tap Storage and select Clear Cache and Clear Data . Restart your device and try downloading the app again. Keeping Your App Store Secure
Using the wrong version can lead to “App not installed” errors or constant crashes. If you want, I can: : Widely considered
While Android 8.1.0 (Oreo) is no longer receiving official security updates from Google, it still supports the Google Play Store