**JavaScript SDK:** [`swarmhit.campaigns.update(campaignId, params)`](/smart-api/sdk/methods#campaigns) Updates any subset of a campaign's writable fields: `name`, `status` (set `active` to start sending, `paused` to stop), the sender pool (`linkedinAccountIds`), the outreach `sequence`, the send `schedule`, `aiInterestEnabled`, the email `unsubscribe` line and `tracking`, and the lead-exclusion rules (`excludeListIds` plus the `exclude*` flags). `sequence` and `schedule` are replaced wholesale — send the complete object you want, not a partial patch of it. A full `sequence` replacement can update the content of any step or A/B variant. For variant A, keep the step's legacy flat copy/media fields identical to the corresponding values in `config.variants[0]`; conflicting values are rejected with `400`. Updating a later variant only requires changing that variant object. For a single existing step or variant, prefer `PATCH /campaigns/{id}/sequence/{stepId}` so unrelated sequence structure cannot be overwritten. Once a campaign has leads in progress, the `sequence` may only be edited safely: you can change step messages and delays and append new steps, but removing, reordering or retyping existing steps is rejected with `400` (a lead's progress is pinned to a step id). Duplicate the campaign to rework its sequence from scratch. An `active` campaign must keep at least one sender: sending an empty `linkedinAccountIds` while the campaign is (or is being set) `active` is rejected with `400`. A campaign won't go `active` while a step has nothing to send: a `message`, `inmail`, `email` or `whatsapp_message` variant with no text (a file alone will do on a `message` or `whatsapp_message`), a `voice_note` without its recording, an `ai_voice_note` without its script, or the first `email` of a path without a subject. That is a `400` with `code: empty-step`: `message` names the steps by their number in the sequence, and `details.steps` lists them (`[{ id, type }]`) to fix with `PATCH /campaigns/{id}/sequence/{stepId}`. Once a campaign has been launched, a `sequence` that empties a step is refused the same way. With accounts of senders in its pools, a campaign won't go `active`, nor an active one change its pools, while a sender (or an account without one on the primary channel: LinkedIn when the sequence has a LinkedIn step or no step, else email, else WhatsApp) has no account on a channel the sequence uses and no account without a sender is there to share: a `400` with `code: sender-no-mailbox` or `sender-no-whatsapp`. Attaching senders with `senderIds` has its own refusals, listed there.