sendEnvelope
open suspend override fun sendEnvelope( conversationId: <Error class: unknown class>, envelope: <Error class: unknown class>, messageTarget: MessageTarget): <Error class: unknown class><<Error class: unknown class>, MessageSent>
Send a Proteus MessageEnvelope to the given conversationId.
Return
Either.Right with the server date time in case of success
Either.Left of a ProteusSendMessageFailure if the server rejected the message
Either.Left of other CoreFailure for more generic cases