# Fill a List from a Segment

`POST /v1/lists/{id}/members`

- Authentication: required (Bearer token)
- Required scope: `api.lists.manage`

Copies a Segment's **current** members into the List, as a
point-in-time snapshot. `{id}` resolves as a List id or its org-unique
key; `segment` as a Segment id or its key.

**This is a snapshot, not a subscription.** A Segment is a live
predicate re-evaluated as contact data changes; a List is an assignment
log. Nothing re-runs this call, and the List does not track the Segment
afterwards — a drip workflow with `add to list` is the standing version
of the same idea.

**Additive only.** Members the Segment does not match are left in the
List, and members already in it are counted in `already_members` and
left alone. So `member_count` can exceed `added + already_members`.
Removing members is the contacts surface.

## Path parameters

- `id` (string, required) — The List's UUID or, when the value does not parse as a UUID, its org-unique key. Unknown handles read as `404 not_found`. Accepted on every List route, read and write alike.

## Request body

Content type: `application/json`

```json
{
  "segment": "string"
}
```

## Example request

```bash
curl -X POST 'https://api.sendops.dev/v1/lists/string/members' \
  -H "Authorization: Bearer $SENDOPS_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"segment":"string"}'
```

## Responses

### 200 — The fill result

Content type: `application/json`

```json
{
  "list_id": "00000000-0000-0000-0000-000000000000",
  "segment_id": "00000000-0000-0000-0000-000000000000",
  "segment_key": "string",
  "added": 0,
  "already_members": 0,
  "member_count": 0
}
```

### 401 — Missing, malformed, or unknown API key

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```

### 403 — Key lacks the required scope or plan limit violated

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```

### 404 — Resource not found

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```

### 422 — A query parameter, path value or body field failed validation.

The body is a `validation_failed` Problem. When the refusal is about a
reference — a segment key, template slug, topic or attribute name the
organization does not have — it additionally carries `validation_code`,
`field`, `line`/`column`, `missing`, `candidates` and `next_step`, so a
client can correct the call without a second round of guessing. See
`ValidationProblem`.

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ],
  "validation_code": "invalid_syntax",
  "field": "string",
  "line": 0,
  "column": 0,
  "missing": [
    {
      "kind": "segment",
      "key": "string"
    }
  ],
  "candidates": {},
  "next_step": "string"
}
```

### 429 — Per-org rate limit exceeded

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```

### 500 — Unexpected server-side failure. The `code` is `internal_error`. The
`request_id` field can be quoted to SendOps support to investigate.

Content type: `application/problem+json`

```json
{
  "type": "https://example.com",
  "title": "string",
  "status": 0,
  "detail": "string",
  "code": "invalid_key",
  "request_id": "string",
  "retry_after": 0,
  "retention_days": 0,
  "scope": "string",
  "resource": "string",
  "errors": [
    {
      "field": "string",
      "reason": "string"
    }
  ],
  "attribute_id": "00000000-0000-0000-0000-000000000000",
  "content_hash": "string",
  "differs": [
    "string"
  ]
}
```