What is a failover DID? How does it work?

What is a failover DID? How does it work?

Every toll free number is associated with 2 DIDs (Destination IDs) namely Primary and Secondary (Failover) DID. Whenever, a customer calls on your toll free number, the call lands on the primary DID. If however, the primary DID breaks down or isn’t working then, the call lands on the secondary i.e. failover DID.