Resolve a contact id (e.g. an @lid) to a phone number — best-effort

GET 
/api/sessions/:sessionId/contacts/:contactId/phone

Resolve a contact id (e.g. an @lid) to a phone number — best-effort

Request

Responses

200

Resolved phone number (MSISDN digits), or null when the engine cannot map it

409

The session is not connected — an engine exists for it but is not ready: disconnected, reconnecting, or still initializing, so the request never reached WhatsApp. Wait for ready and retry. A session that was never started answers 400 instead, and the session lifecycle routes answer 409 for a conflicting state rather than this. One window answers this while the session still reads ready: WhatsApp Web periodically reloads its own page and the engine re-injects into it — for those few seconds the answer is a 409 naming the reload; retry shortly.