character_id with Create Session from Character to start a session.
Provide a nonempty avatars[].persona for each avatar when creating or updating a character. Describe its identity, speech, movement, and listening behavior together; Vivix prepares the character’s behavior automatically when a session starts. See Persona examples for sample Personas.
Response envelope. REST responses are wrapped in {code, message, data}: code = 0 means success. Field descriptions below refer to fields inside data.