# POST /api/v1/api-clients/{client_pk}/signing-keys

> Add API client signing key

- **Tag:** api-clients
- **Operation ID:** `add_api_client_signing_key`

## Description

Add a request-signing key. For `hmac-sha256` DayZero generates the secret and returns it once; for `ed25519` send the public key. Step-up.

## Authentication

Bearer token in `Authorization` header.
Required header: `x-business-id: <business uuid>`.

## Parameters

- `client_pk` (path, string, required)

## Request body

Schema: `ApiClientSigningKeyCreate`

- `alg` (string · required) (one of: hmac-sha256, ed25519) — `hmac-sha256`: DayZero generates a shared secret and returns it once. `ed25519`: send your public key in `public_key`.
- `kid` (string) — Key id sent as X-DZ-Key-Id; generated when omitted.
- `public_key` (string) — Ed25519 only: the raw 32-byte public key, base64 or base64url.

## Example request

```json
{
  "alg": "hmac-sha256",
  "kid": "sk-2026-10"
}
```

## Responses

### 201 — Successful Response

Schema: `SuccessEnvelope_ApiClientSigningKeyCreateResponse_`

- `success` (boolean)
- `message` (string)
- `code` (string)
- `data` (ApiClientSigningKeyCreateResponse)

### 400 — Bad Request - Invalid input

Schema: `ErrorResponse`

- `error` (string · required) — Error category: `validation_error`, `unauthorized`, `forbidden`, `not_found`, `conflict`, `rate_limited`, `server_error`, or `service_unavailable`.
- `message` (string · required) — Human-readable explanation, safe to show to end users.
- `code` (string · required) — Stable machine-readable code in `CATEGORY_NNN` form (e.g. `NOT_FOUND_006`, `AUTH_010`, `GEN_002`).
- `request_id` (string) — Correlation id for support requests. Echoes the `x-request-id` request header when one was supplied.
- `errors` (object) — Field-level validation messages keyed by field name. Present on 400/422 validation failures only.

### 401 — Unauthorized - Missing or expired token, an MCP OAuth token used against the REST API, or no access to this business

Schema: `ErrorResponse`

- `error` (string · required) — Error category: `validation_error`, `unauthorized`, `forbidden`, `not_found`, `conflict`, `rate_limited`, `server_error`, or `service_unavailable`.
- `message` (string · required) — Human-readable explanation, safe to show to end users.
- `code` (string · required) — Stable machine-readable code in `CATEGORY_NNN` form (e.g. `NOT_FOUND_006`, `AUTH_010`, `GEN_002`).
- `request_id` (string) — Correlation id for support requests. Echoes the `x-request-id` request header when one was supplied.
- `errors` (object) — Field-level validation messages keyed by field name. Present on 400/422 validation failures only.

### 403 — Forbidden - Insufficient permissions

Schema: `ErrorResponse`

- `error` (string · required) — Error category: `validation_error`, `unauthorized`, `forbidden`, `not_found`, `conflict`, `rate_limited`, `server_error`, or `service_unavailable`.
- `message` (string · required) — Human-readable explanation, safe to show to end users.
- `code` (string · required) — Stable machine-readable code in `CATEGORY_NNN` form (e.g. `NOT_FOUND_006`, `AUTH_010`, `GEN_002`).
- `request_id` (string) — Correlation id for support requests. Echoes the `x-request-id` request header when one was supplied.
- `errors` (object) — Field-level validation messages keyed by field name. Present on 400/422 validation failures only.

### 404 — Not Found - Resource does not exist

Schema: `ErrorResponse`

- `error` (string · required) — Error category: `validation_error`, `unauthorized`, `forbidden`, `not_found`, `conflict`, `rate_limited`, `server_error`, or `service_unavailable`.
- `message` (string · required) — Human-readable explanation, safe to show to end users.
- `code` (string · required) — Stable machine-readable code in `CATEGORY_NNN` form (e.g. `NOT_FOUND_006`, `AUTH_010`, `GEN_002`).
- `request_id` (string) — Correlation id for support requests. Echoes the `x-request-id` request header when one was supplied.
- `errors` (object) — Field-level validation messages keyed by field name. Present on 400/422 validation failures only.

### 422 — Validation Error

Schema: `ErrorResponse`

- `error` (string · required) — Error category: `validation_error`, `unauthorized`, `forbidden`, `not_found`, `conflict`, `rate_limited`, `server_error`, or `service_unavailable`.
- `message` (string · required) — Human-readable explanation, safe to show to end users.
- `code` (string · required) — Stable machine-readable code in `CATEGORY_NNN` form (e.g. `NOT_FOUND_006`, `AUTH_010`, `GEN_002`).
- `request_id` (string) — Correlation id for support requests. Echoes the `x-request-id` request header when one was supplied.
- `errors` (object) — Field-level validation messages keyed by field name. Present on 400/422 validation failures only.

## Code samples

### cURL

```bash
curl -X POST 'https://api.ondayzero.com/api/v1/api-clients/{client_pk}/signing-keys' \
  -H 'Authorization: Bearer dz_your_token' \
  -H 'x-business-id: YOUR_BUSINESS_ID' \
  -H 'Content-Type: application/json' \
  -d '{
  "alg": "hmac-sha256",
  "kid": "sk-2026-10"
}'
```

### JavaScript

```javascript
const response = await fetch('https://api.ondayzero.com/api/v1/api-clients/{client_pk}/signing-keys', {
  method: 'POST',
  headers: {
    Authorization: 'Bearer dz_your_token',
    'x-business-id': 'YOUR_BUSINESS_ID',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
  "alg": "hmac-sha256",
  "kid": "sk-2026-10"
}),
});
const data = await response.json();
```

### Python

```python
import httpx

headers = {
    "Authorization": "Bearer dz_your_token",
    "x-business-id": "YOUR_BUSINESS_ID",
}

payload = {'alg': 'hmac-sha256', 'kid': 'sk-2026-10'}

response = httpx.post("https://api.ondayzero.com/api/v1/api-clients/{client_pk}/signing-keys", headers=headers, json=payload)
data = response.json()
```

## See also

- HTML version: https://www.ondayzero.com/docs/reference/api-clients/add-api-client-signing-key
- OpenAPI slice: https://www.ondayzero.com/docs/reference/api-clients/add-api-client-signing-key/openapi.json
- Other endpoints in **api-clients**: https://www.ondayzero.com/docs/reference/api-clients (markdown bundle: https://www.ondayzero.com/docs/reference/api-clients.md, OpenAPI: https://www.ondayzero.com/docs/reference/api-clients/openapi.json)
- Endpoint catalog: https://www.ondayzero.com/docs/reference/index.md