How to set up From Option for Transactional Messaging via REST API? It seems that it is set up by default of definition creation.
and I can see that the only way to select this field is via the send definition in the UI [https://help.salesforce.com/articleView?id=mc_es_create_send_classification.htm&type=5]
However, for Send definitions created from the API, this is not populated in the UI.
Thanks for your clarification.