Publishes the draft sequence, making it the graph the campaign runs. Also enrols any leads that were added before a sequence existed. Steps keep their ids across publishes, so in-flight leads resume where they were.

Every step is re-validated first — publishing is the last gate before real emails go out, and a step written from the campaign builder never passed Add or Update Step. A step missing a required field (a send with no subject or body, say) fails the publish with a 400 naming it, rather than shipping a blank email.

The campaign still needs state to be active to send — use Resume Campaign.