---
updatedAt: 2026-07-07T17:42:21.000Z
agentTools:
  projectIndex: https://docs.bynn.com/llms.txt
---

# Start a liveness capture

Start a liveness capture for the session identified by :session_id. Run this to get the credentials for the liveness capture SDK.

# OpenAPI definition

```json
{
  "openapi": "3.0.0",
  "info": {
    "title": "BYNN API",
    "description": "The BYNN API is organized around REST. Our API has predictable, resource-oriented URLs, and uses HTTP response codes to indicate API errors. We use built-in HTTP features, like HTTP authentication and HTTP verbs, which are understood by off-the-shelf HTTP clients. We support cross-origin resource sharing, allowing you to interact securely with our API from a client-side web application (though you should never expose your secret API key in any public website’s client-side code). JSON is returned by all API responses, including errors, although our API libraries convert responses to appropriate language-specific objects. To make the API as explorable as possible, accounts have test mode and live mode API keys. There is no “switch” for changing between modes, just use the appropriate key to perform a live or test transaction. Requests made with test-mode credentials never hit live networks and incur no cost. **AUTHENTICATION:** Please use your **Private API Key** that looks like this `private_Nv7UpwQbSmWtUTiSWfw1bdHm` as the username and password in HTTP basic auth.",
    "termsOfService": "https://bynn.com/terms",
    "contact": {
      "name": "BYNN Development Team",
      "email": "hello@bynn.com",
      "url": "https://docs.bynn.com"
    },
    "license": {
      "name": "BYNN Documentation",
      "url": "https://docs.bynn.com"
    },
    "version": "1.0"
  },
  "tags": [
    {
      "name": "sessions",
      "description": "Operations about sessions"
    }
  ],
  "paths": {
    "/sessions/{session_id}/liveness/start": {
      "post": {
        "summary": "Start a liveness capture",
        "description": "Start a liveness capture for the session identified by :session_id. Run this to get the credentials for the liveness capture SDK.",
        "parameters": [
          {
            "in": "path",
            "name": "session_id",
            "description": "Unique session token",
            "required": true,
            "schema": {
              "type": "string"
            }
          }
        ],
        "responses": {
          "201": {
            "description": "Start a liveness capture",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Bynn_V1_Entities_LivenessStart"
                }
              }
            }
          },
          "400": {
            "description": "Could not start liveness",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Bynn_V1_Entities_Error"
                }
              }
            }
          },
          "404": {
            "description": "Invalid session",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/Bynn_V1_Entities_Error"
                }
              }
            }
          }
        },
        "tags": [
          "sessions"
        ],
        "operationId": "postSessionsSessionIdLivenessStart"
      }
    }
  },
  "servers": [
    {
      "url": "//api.bynn.com/v1"
    }
  ],
  "components": {
    "schemas": {
      "Bynn_V1_Entities_Error": {
        "type": "object",
        "properties": {
          "error": {
            "type": "object",
            "properties": {
              "type": {
                "type": "string",
                "example": "validation_error",
                "description": "Type of error"
              },
              "message": {
                "type": "string",
                "example": "Invalid parameters",
                "description": "Error message"
              }
            },
            "required": [
              "type",
              "message"
            ]
          }
        },
        "required": [
          "error"
        ],
        "description": "Bynn_V1_Entities_Error model"
      },
      "Bynn_V1_Entities_LivenessStart": {
        "type": "object",
        "properties": {
          "age_verification_id": {
            "type": "string",
            "description": "Age Verification ID"
          },
          "liveness_session": {
            "allOf": [
              {
                "$ref": "#/components/schemas/Bynn_V1_Entities_LivenessSession"
              }
            ],
            "description": "Liveness session information"
          }
        },
        "required": [
          "age_verification_id",
          "liveness_session"
        ],
        "description": "Bynn_V1_Entities_LivenessStart model"
      },
      "Bynn_V1_Entities_LivenessSession": {
        "type": "object",
        "properties": {
          "session_id": {
            "type": "string",
            "description": "Liveness session identifier"
          },
          "credentials": {
            "allOf": [
              {
                "$ref": "#/components/schemas/Bynn_V1_Entities_LivenessCredentials"
              }
            ],
            "description": "Credentials"
          },
          "server_time": {
            "type": "integer",
            "format": "int32",
            "description": "Server time in milliseconds"
          }
        },
        "required": [
          "session_id",
          "credentials",
          "server_time"
        ]
      },
      "Bynn_V1_Entities_LivenessCredentials": {
        "type": "object",
        "properties": {
          "id": {
            "type": "string",
            "description": "Access ID"
          },
          "access_key": {
            "type": "string",
            "description": "Access Key"
          },
          "token": {
            "type": "string",
            "description": "Access Session Token"
          }
        },
        "required": [
          "id",
          "access_key",
          "token"
        ]
      }
    }
  }
}
```