Adds leads to a campaign. Each lead needs an email; any other keys must match the campaign's lead_schema (see Get Campaign) and are otherwise ignored and reported in dropped_fields — register custom fields first with Update Lead Schema. Re-adding an existing address updates it instead of duplicating, so retries are safe. Accepts up to 1000 leads per call.

Rows without a usable email are skipped, not fatal — they are counted in skipped and the rest of the batch is still added. The call only fails if no row has one.

Enrolment. Leads enrol as soon as the campaign has a published sequence, whether or not it is active — a lead added to a paused campaign becomes in_sequence with its next step held, and starts moving on Resume Campaign. Leads only stay at added when no sequence is published yet; Publish Sequence then picks them up.