# Preview a recurring series (/docs/api-reference/scheduling-series/preview-scheduling-series)

Which occurrences would be free, without booking anything.

`POST https://api.coss.com/v1/scheduling/series/preview`

Authenticate with your API key as a bearer token (`Authorization: Bearer coss_test_…`). Responses are JSON with snake_case fields; errors are `{ error: { type, code, message, param?, issues?, request_id } }` (https://coss.com/docs/api-reference/errors.md).

## Request body

- `event_type` (string, required): The event type's id or uid.
- `start` (string, required): An ISO 8601 instant with an offset.
- `host` (string): A specific host (id or uid). Default: chosen fairly from those free.
- `attributes` (map of string | string[]): Only choose among pool hosts matching all of these.
- `duration_minutes` (integer, 5-1440): One of the event type's `duration_options`.
- `attendee` (object, required): Name and email are only needed if coss.com notifies this attendee.
  - `uid` (string, 1-255 characters): Your own id for this person, used to erase their data later.
  - `name` (string, 1-100 characters)
  - `email` (string, email, at most 320 characters)
  - `phone` (string)
  - `time_zone` (string, required, 1-64 characters): An IANA time zone name.
  - `locale` (string, 2-35 characters)
- `answers` (map of string | string[]): Answers to the event type's questions. Stored encrypted, and returned only by retrieving the booking.
- `location` (object): One of the event type's `locations`, with your link filled in if it has none.
  - One of (1):
    - `type` ("link", required)
    - `url` (string | null, uri, at most 2000 characters, default null)
  - One of (2):
    - `type` ("phone", required)
    - `number` (string | null, at most 32 characters, default null)
  - One of (3):
    - `type` ("in_person", required)
    - `address` (string | null, at most 500 characters, default null)
  - One of (4):
    - `type` ("google_meet", required)
  - One of (5):
    - `type` ("microsoft_teams", required)
- `metadata` (map of string): Your own key-value pairs. Don't put sensitive data here.
- `recurrence` (object, required)
  - `frequency` ("weekly" | "monthly", required)
  - `interval` (integer, 1-12, default 1)
  - `count` (integer, required, 2-52)
- `on_conflict` ("reject" | "skip", default "reject"): If an occurrence isn't free: book nothing, or book the rest and report it.

## Example request

TypeScript (the `coss` package):

```ts
import { Coss } from "coss";

const coss = new Coss({
  apiKey: process.env.COSS_API_KEY,
  baseUrl: "https://api.coss.com",
});

const { data, error } = await coss.scheduling.series.preview({
  event_type: "evtype_01kd2m9a0b1c2d3e4f5g6h7j8m",
  start: "2027-01-04T15:00:00.000Z",
  attendee: {
    uid: "patient_77",
    time_zone: "America/New_York",
  },
  recurrence: {
    frequency: "weekly",
    interval: 1,
    count: 12,
  },
});
```

HTTP:

```sh
curl -X POST "https://api.coss.com/v1/scheduling/series/preview" \
  -H "Authorization: Bearer $COSS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "event_type": "evtype_01kd2m9a0b1c2d3e4f5g6h7j8m",
  "start": "2027-01-04T15:00:00.000Z",
  "attendee": {
    "uid": "patient_77",
    "time_zone": "America/New_York"
  },
  "recurrence": {
    "frequency": "weekly",
    "interval": 1,
    "count": 12
  }
}'
```

## Response 200

Each occurrence.

- `object` ("list", required)
- `data` (object[], required)
  - `start` (string, required)
  - `available` (boolean, required)
  - `reason` (string | null, required)
  - `hosts` (string[], required)
- `has_more` (false, required)

Example:

```json
{
  "object": "list",
  "data": [
    {
      "start": "2027-01-04T15:00:00.000Z",
      "available": true,
      "reason": null,
      "hosts": [
        "host_01kd2m9a0b1c2d3e4f5g6h7j8m"
      ]
    }
  ],
  "has_more": false
}
```

## Errors

- `400`: The body is not valid JSON (`invalid_json`). Also when the `Coss-Version` header names an unknown API version (`invalid_api_version`).
- `401`: The API key is missing, invalid, revoked or expired (`authentication_error`).
- `403`: The API key lacks the permission this endpoint needs (`permission_error`), or its organization is suspended (`organization_suspended`).
- `404`: Nothing with this id or uid exists in the environment (`not_found`).
- `415`: The body is not sent as `application/json` (`unsupported_media_type`).
- `422`: The request failed validation (`validation_error`, see `issues`), or can't be done: see `code`.
- `429`: Too many requests with this API key (`rate_limited`), or too many requests with invalid keys from this address (`too_many_failed_authentications`). Retry after `Retry-After` seconds. Successful responses carry `RateLimit-Limit`, `RateLimit-Remaining` and `RateLimit-Reset` (seconds until the limit is fully restored).
- `500`: Unexpected server error (`api_error` / `internal_error`).
- `503`: The API key could not be verified right now; retry (`service_unavailable`).