Authentication failed means there is a temporary block due to too many failed attempts. After 30 minutes after the last login attempt, the block is removed automatically by the system. You can also contact our Sync support team at help@sync.com to remove it for you.
See Also
How to Fix Wi-Fi Authentication Problems on AndroidUnderstanding Authentication, Authorization, and Encryption : TechWeb : Boston UniversityWi-Fi not working? How to fix the most common Wi-Fi problems | Digital TrendsHow to Fix the “Google Play Authentication Is Required” Error on Android
If you have forgotten your password see:
https://www.sync.com/help/what-do-i-do-if-i-forget-my-password/
