conversationId

Optional. Identifier of the conversation. Generally it's auto generated by Google. Only set it if you cannot wait for the response to return a auto-generated one to you. The conversation ID must be compliant with the regression fomula "a-zA-Z*" with the characters length in range of 3,64. If the field is provided, the caller is resposible for 1. the uniqueness of the ID, otherwise the request will be rejected. 2. the consistency for whether to use custom ID or not under a project to better ensure uniqueness.