# Start a WebRTC call

Exchange an SDP offer for an answer to open a Nur call.

`POST https://api.eesi.ai/v1/realtime/calls`

Create a WebRTC call. OpenAI SDKs receive an application/sdp answer.

A phone or a browser may open it with a client secret instead of a key
(``Authorization: Bearer <secret>``), as with OpenAI's ephemeral keys: the
secret is spent here and the call is the session it binds, with its locks,
limits, webhook and data settings.

Parameters:

- `model` (query)
- `timezone` (query)
- `source` (query)
- `resume` (query)
- `resume_token` (query)

Request body: multipart/form-data, application/sdp, application/json.

- `sdp` (string, required)
- `session` (object): OpenAI Realtime session configuration

Responses: 201, 400, 404.

Schemas: https://docs.eesi.ai/api-reference/public.json