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`.