Send Campaign

Queues the given Campaign for sending to all subscribed members of its associated CustomerSegment. Members with a non-null unsubscribed_at are excluded. Individual CampaignSend records are created for each recipient and processed asynchronously.

The CampaignContent used for each recipient's CampaignSend is selected based on the customer's preferred_locale, falling back to the site's locale if no CampaignContent exists for the customer's preferred locale.

Returns 202 Accepted immediately; use the listCampaignSends endpoint to track delivery progress.