Launch a campaign

Freezes the audience and sets the campaign to send — now, or at scheduledAt (up to a year ahead). More than 60 seconds in the future, the campaign becomes scheduled; otherwise it starts building the recipient list at once.

It does not take an Idempotency-Key: a second launch answers 409, because the campaign is no longer a draft.

With an API key limited to some numbers, the audience — saved or typed as a filter — is narrowed to the contacts that have a conversation on those numbers, and that slice is frozen at launch together with the audience. A campaign launched by an unrestricted key goes to the whole base.