A. Ensure that you have a stable internet connection. Try switching between Wi-Fi and mobile data. Clear the app cache by going to Settings > Apps > Vélib' > Storage > Clear Cache. Restart the app and attempt to sign up again.

B. Check if the app is updated to the latest version. Go to the Google Play Store, search for Vélib', and see if an update is available. If so, update the app and try signing up again.