# POST Validate setting the default customiser language

Dry-run a set-default without changing anything. The response on the failing path is exactly the `language_not_defaultable` problem the write would return, with the same `reason`. On a language that would become the default, the response is a 200 `customiser_language_validation` confirmation. Nothing is written, no caches are touched, no idempotency key is consumed, and no activity is recorded. The verdict is advisory: nothing binds it to a later write, and the language can legitimately change between the two calls. Requires the `customisers:write` scope, because it is the write dry-run twin. 401, 403, 404, 422, and 429 problems behave exactly as on the set-default operation.

- Source URL: https://www.signcustomiser.com/help/api/v3-post-validate-setting-the-default-customiser-language/
- Markdown URL: https://www.signcustomiser.com/help/api/v3-post-validate-setting-the-default-customiser-language.md
- Group: Customiser languages
- Method: POST
- Path: /api/v3/customisers/{customiser_id}/languages/{language_code}/validate-default
- Auth: Bearer token
- Required scopes: `customisers:write`

## Path parameters

- customiser_id (string, required): The customiser id, from the list customisers operation. Example: 1
- language_code (string, required): The language tag, from the list customiser languages operation. Example: fr

## cURL example

```bash
curl https://web.signcustomiser.com/api/v3/customisers/1/languages/fr/validate-default \
  --request POST \
  --header 'Accept: application/json' \
  --header 'Authorization: Bearer YOUR_API_TOKEN'
```

## Response examples

### 200 Set default would apply

```json
{
  "data": {
    "object": "customiser_language_validation",
    "operation": "make_default",
    "customiser_id": 42,
    "language_code": "fr",
    "valid": true
  },
  "links": {
    "self": "https://web.signcustomiser.com/api/v3/customisers/42/languages/fr/validate-default",
    "documentation": "https://www.signcustomiser.com/help/api/"
  },
  "meta": {
    "api_version": "v3",
    "request_id": "req_01jz9x2k7c8f3m5n6p7q8r9s0t"
  }
}
```

### 403 Insufficient scope

```json
{
  "type": "https://www.signcustomiser.com/help/api/problems/insufficient_scope",
  "title": "Insufficient scope",
  "status": 403,
  "code": "insufficient_scope",
  "detail": "This operation requires the customisers:write scope, but the API key grants the following scopes: customisers:read. Create a key that includes the required scope in the merchant admin under Integrate → API Tokens.",
  "required_scopes": [
    "customisers:write"
  ],
  "granted_scopes": [
    "customisers:read"
  ],
  "request_id": "req_01jz9x2k7c8f3m5n6p7q8r9s0t"
}
```

### 422 Language not published

```json
{
  "type": "https://www.signcustomiser.com/help/api/problems/language_not_defaultable",
  "title": "Language not eligible to be the default",
  "status": 422,
  "code": "language_not_defaultable",
  "detail": "The default language is the source every other language is translated from, so it must be published and carry a current published value for every required key. Publish this language first, then retry.",
  "reason": "not_published",
  "request_id": "req_01jz9x2k7c8f3m5n6p7q8r9s0t"
}
```