A. Check your payment method to ensure it is valid and has sufficient funds. If you are using a credit card, verify that it is not expired and that your billing information is correct. You can also try removing and re-adding your payment method in the Google Play Store settings.
B. Clear the cache and data for the Google Play Store app. Go to Settings > Apps > Google Play Store > Storage > Clear Cache and Clear Data. Restart your device and try the payment again.