Function request 

pub fn request(
    workflow: &str,
    key: &str,
    event: &Event,
) -> (&'static str, String, Value, Value)

One event as an update-with-start, for any client (the engine, the server’s Client, the SDKs): the coordinator’s workflow type, its ID, its start input, and the EVENT update’s argument. Send it with the running policy use-existing, the event ID as the update ID, and send it again when the answer is ENDED.