Create an alphanumeric sender ID

Registers an alphanumeric sender ID (e.g. ZERNIO) — a branded from for one-way international SMS. No phone number purchase or carrier registration is needed; once created, pass it as from on POST /v1/sms/messages.

Constraints: 3-11 characters (letters, digits, spaces; at least one letter). Sends cannot reach the US, Canada, or Puerto Rico, are text-only, and recipients cannot reply. Sender IDs that impersonate well-known brands or institutions are rejected. Names are not exclusive: the same sender ID can be registered by any number of workspaces. Creating the same sender ID again is a no-op (re-activates it after a delete).