When your phone fails to complete a payment at the store, first check if NFC is enabled in settings. Sometimes the feature gets disabled accidentally after system updates. Hold your device closer to the terminal and make sure you're not moving it away too quickly. The connection needs 2-3 seconds to process. If your default card changed somehow, open the app and verify which card is set for tap-to-pay transactions.
This usually happens after major Android updates. Go to Settings, find Samsung Wallet in the apps list, and clear both cache and data. You'll need to add your cards again, but this solves most stability issues. Make sure your phone's software is fully updated too. If crashes continue, uninstall and reinstall the application completely.
Poor internet connection is the main culprit here. Switch between Wi-Fi and mobile data to see which works better. The app stores some transaction data locally, but syncing requires stable connection. If you're on mobile data, check if background data isn't restricted for this app in system settings. Sometimes carriers' networks have temporary routing issues that affect specific services.
Recalibrate your fingerprint in phone's biometric settings. Fingers change slightly with temperature and moisture, so register the same finger multiple times at different angles. For PIN issues, you'll need to reset it through the app's security settings. Make sure your screen protector isn't too thick, as this interferes with fingerprint sensor accuracy.