Go to WAN General Setup  then configure WAN1

2. On WAN1 Enable : Yes, Active Mode: Always On, and Backup:WAN3

3. On WAN2 Enable : Yes, Active Mode: Always On, and Backup:WAN3

4. On WAN3 Enable : Yes, Active Mode: Backup, and Backup Type :When all WAN Disconnect

5. Now go to Load Balancing then tick Index 1

6. Tick Enable, Protocol: Any, Binding WAN Interface:WAN1, Tick Auto Failover to other WAN

7. On the System Status WAN should show that WAN1 and WAN2 is connected

8. Now go to Online Status

9. When WAN1 disconnects the connection goes to WAN2

10. When WAN2 also disconnects the connection goes to WAN3