## POST /api/v2/domains/{id}/billing-cycle

**Change domain billing period**

Change the renewal period for one domain. Get `{id}` from `GET /api/v2/domains` `data[].id` and read `GET /api/v2/domains/{id}/billing-cycle` immediately first. Send only a period that appears in that GET response's `options[]`; supported year counts vary by TLD/product and clients must not invent 1-9 year periods. Send `billingCycle` for canonical 1, 2, or 3 year rows (`annually`, `biennially`, `triennially`) or `periodYears` for a returned longer row where `billingCycle` is null. If both are sent, they must refer to the same period. The route returns 409 `existing_invoice_blocking` when a pending renewal order, pending domain order, or outstanding invoice blocks the change; use the `pendingRenewalOrder`, `pendingOrder`, and `existingInvoice` fields in the Problem Details `extensions` to resolve the blocker.

### Related Endpoints

- `GET /api/v2/domains/{id}/billing-cycle`: Get domain billing-period options
- `GET /api/v2/domains/{id}`: Get domain details
- `GET /api/v2/domains/{id}/renewal`: Get domain renewal state

### Headers

- `Accept`: application/json
- `Authorization`: Bearer YOUR_API_KEY
- Required API scopes: `write:domains`, `write:billing`
- `Content-Type`: application/json

### Parameters

- `id` (path, string, required): Public domain ID from `GET /api/v2/domains` `data[].id`. Do not invent this value; use the exact ID returned by the referenced API response. Example: `dom_01hxa3b4c5d6e7f8g9h0j1k2m3`

### Request Body

- `billingCycle` (string, optional): Canonical period slug for 1, 2, or 3 years. Example: `biennially`
  Allowed values: annually, biennially, triennially
- `periodYears` (integer | string, optional) [min: 1, max: 9]: Domain renewal period in years. Use this only for a row returned by GET where `billingCycle` is null; not every TLD offers every 1-9 year period. Example: `5`

### Request Examples

#### Change to two-year renewal

```bash
curl -X POST "https://cloud.hostup.se/api/v2/domains/dom_01hxa3b4c5d6e7f8g9h0j1k2m3/billing-cycle" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Accept: application/json" \
  -H "Content-Type: application/json" \
  -d '{
    "billingCycle": "biennially"
  }'
```

```json
{
  "billingCycle": "biennially"
}
```

#### Change to a returned five-year renewal

```bash
curl -X POST "https://cloud.hostup.se/api/v2/domains/dom_01hxa3b4c5d6e7f8g9h0j1k2m3/billing-cycle" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Accept: application/json" \
  -H "Content-Type: application/json" \
  -d '{
    "periodYears": 5
  }'
```

```json
{
  "periodYears": 5
}
```

### Response Schema

- `billing` (object, optional)
- `billing.amount` (number, required) Example: `159`
- `billing.currencyCode` (string, required) Example: `SEK`
- `billing.billingCycle` (string,null, required): Canonical cycle slug for 1-3 year periods. Four- to nine-year domain periods return null and use periodYears. Example: `annually`
  Allowed values: annually, biennially, triennially, 
- `billing.periodYears` (integer,null, required) Example: `1`
- `billing.initialAmount` (number, optional): First-period amount when it differs from the recurring amount. Example: `99`

### Responses

#### 200 - Updated billing object.
```json
{
  "billing": {
    "amount": 318,
    "currencyCode": "SEK",
    "billingCycle": "biennially",
    "periodYears": 2
  }
}
```

#### 400 - Invalid request. The response body is an RFC 7807 Problem Details document.
```json
{
  "type": "https://developer.hostup.se/errors/invalid_request",
  "title": "Invalid request",
  "status": 400,
  "detail": "The request body failed validation.",
  "code": "invalid_request",
  "instance": "/api/v2/resource",
  "requestId": "req_01hxa3b4c5d6e7f8g9h0j1k2m3",
  "timestamp": "2026-04-27T12:34:56.000Z",
  "errors": [
    {
      "pointer": "/items/0/domainName",
      "detail": "`domainName` is required.",
      "code": "invalid_request"
    }
  ]
}
```

#### 401 - Unauthorized. Authentication is required.
```json
{
  "type": "https://developer.hostup.se/errors/unauthorized",
  "title": "Unauthorized",
  "status": 401,
  "detail": "Authentication is required.",
  "code": "unauthorized",
  "instance": "/api/v2/resource",
  "requestId": "req_01hxa3b4c5d6e7f8g9h0j1k2m3",
  "timestamp": "2026-04-27T12:34:56.000Z"
}
```

#### 403 - Forbidden. The caller lacks a required scope or does not own the resource.
```json
{
  "type": "https://developer.hostup.se/errors/forbidden",
  "title": "Forbidden",
  "status": 403,
  "detail": "The caller lacks a required scope or does not own the resource.",
  "code": "forbidden",
  "instance": "/api/v2/resource",
  "requestId": "req_01hxa3b4c5d6e7f8g9h0j1k2m3",
  "timestamp": "2026-04-27T12:34:56.000Z"
}
```

#### 404 - Not found. The resource does not exist or is not owned by the caller.
```json
{
  "type": "https://developer.hostup.se/errors/not_found",
  "title": "Not found",
  "status": 404,
  "detail": "The requested resource could not be found.",
  "code": "not_found",
  "instance": "/api/v2/resource",
  "requestId": "req_01hxa3b4c5d6e7f8g9h0j1k2m3",
  "timestamp": "2026-04-27T12:34:56.000Z"
}
```

#### 429 - Rate limited. Retry after the limit resets. 429 responses include `Retry-After` seconds plus `X-RateLimit-*` headers.
```json
{
  "type": "https://developer.hostup.se/errors/rate_limit_exceeded",
  "title": "Too many requests",
  "status": 429,
  "detail": "Too many requests. Retry after the limit resets.",
  "code": "rate_limit_exceeded",
  "instance": "/api/v2/resource",
  "requestId": "req_01hxa3b4c5d6e7f8g9h0j1k2m3",
  "timestamp": "2026-04-27T12:34:56.000Z"
}
```

#### 500 - Internal error. Retry later or contact support if the issue persists.
```json
{
  "type": "https://developer.hostup.se/errors/internal_error",
  "title": "Internal server error",
  "status": 500,
  "detail": "An unexpected error occurred. Retry later or contact support if the issue persists.",
  "code": "internal_error",
  "instance": "/api/v2/resource",
  "requestId": "req_01hxa3b4c5d6e7f8g9h0j1k2m3",
  "timestamp": "2026-04-27T12:34:56.000Z"
}
```