Email Unsubscribe Groups
Add a group suppression
Creates a suppression with reason: unsubscribe, source: manual, group_id: <this group>. All other body fields are ignored; only to is read. Idempotent (same dedupe key → 200, no new event).
post/email_unsubscribe_groups/{id}/suppressions
Request body
Response
Idempotent — already existed.