OptionalavatarOptionalfirstiMessage display first name shown beside this number's messages in
recipients' Messages apps (max 30 chars). null or "" clears it. Valid only
on numbers with the imessage capability — rejected with 400 otherwise.
OptionalinboundNew system prompt the AI voice agent uses on inbound calls to this number.
OptionalinboundBCP-47 language tag pinning inbound calls to this number to one language. null clears it, so the language reverts to per-call detection from the caller's country prefix.
OptionalinboundVoice gender for inbound calls: "male" or "female". null clears it, so the voice reverts to the default (female).
OptionallastiMessage display last name (max 30 chars); null or "" clears it. iMessage numbers only.
OptionalmaxCap calls on this number to at most this many seconds, applied as a hard ceiling to both inbound calls to the number and outbound calls placed from it. The effective cap on any call is the smallest of the per-number, account, and per-call limits.
OptionalnicknameHuman-readable label for the number, max 100 chars; null or "" clears it.
iMessage avatar photo: a public image URL (downloaded server-side), a local file path, or raw bytes (both uploaded as multipart). jpeg/png/gif/webp, max 5 MB. Replace-only — the photo can't be removed. iMessage numbers only.