With the release of Verify V2's General Availability, Silent Authentication is a channel in the Verify API that enables authentication without a 2FA code by using a mobile phone's Subscriber Identity Module (SIM) to prove a user's identity. To use Silent Authentication, an application must be running on a phone over a mobile network and have a cellular connection established. The Vonage SDKs provide tools for iOS and Android developers to integrate silent auth into their applications. A Silent Authentication Sandbox allows testing of successful verification without the need for a mobile network connection. When using the sandbox, a response containing a request ID and check URL is sent, which must be followed with a GET request to complete the verification process. If Silent Authentication fails due to various reasons such as lack of cellular coverage or Wi-Fi connection, fallback options like SMS can be configured in the workflow. The guide provides detailed information on implementing Silent Authentication and using the sandbox for testing purposes.