> For the complete documentation index, see [llms.txt](https://docs.vida.id/identity-stack/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.vida.id/identity-stack/authentication/authentication-factors/biometric-device-selfie-id/integration-methods/selfie-id-api/api/api-reference/transaction-initiation.md).

# Transaction Initiation

Transaction initiation marks the beginning of a session between the client and the server. This process is triggered when a user needs to provision or authenticate their credentials. In this phase, the server generates a session ID, a user challenge, and a bearer token and the follow up URI which will be used by the client to complete the transaction.