# External order validation
Sometimes, you may need to perform custom validation on orders, as an additional step before the order placement. For example, this could be useful in case you want to support different or more complex validation rules specific to your business logic.
If you want to use the external order validation feature in a [market](https://app.gitbook.com/s/RWJeylueWkzLadK710XZ/markets), fill in the market's `external_order_validation_url` field with your external service endpoint and make sure your service is compliant with the specifications described below.
### Triggering external validation
When you want to validate an order based on your external logic, [update](https://app.gitbook.com/s/RWJeylueWkzLadK710XZ/orders/update) it and set the `_validate` attribute to `true`:
curl -g -X PATCH \
'https://yourdomain.commercelayer.io/api/orders/xYZkjABcde' \
-H 'Accept: application/vnd.api+json' \
-H 'Authorization: Bearer your-access-token' \
-H 'Content-Type: application/vnd.api+json' \
-d '{
"data": {
"type": "orders",
"id": "xYZkjABcde",
"attributes": {
"_validate": true
}
}
}'
Upon this call, Commerce Layer triggers a `POST` request to the specified `external_validation_url` endpoint, sending the order payload (including the related line items) in the request body.
{% hint style="info" %}
To check if an external order validation has been triggered you can inspect the order's `validations_count` attribute and make sure it gets incremented.
{% endhint %}
{% hint style="warning" %}
If the external validation fails the API responds to the `PATCH` above with a `422` error, showing the message(s) that your logic has returned. Please note that **the order is not marked as invalid and can still be placed** (in case it passes the standard, automatic validation at the time of placement). External validation errors are stored (until order approval) in [resource errors](https://app.gitbook.com/s/RWJeylueWkzLadK710XZ/resource_errors) which cannot be fetched by a sales channel (e.g. directly from the customer), so it's up to the client side to warn customers about them.
{% endhint %}
### Request
The request payload is a [JSON:API](https://jsonapi.org)-compliant object you can query to perform your own computation. Aside from the **target resource** — `order` in this specific case — some **relationships** are also included to avoid useless API roundtrips:
* `billing_address`
* `shipping_address`
* `line_items.item`
* `line_items`
* `market`
* `customer`
* `shipments`
* `shipments.shipping_method`
{
"data": {
"id": "wBXVhKzrnq",
"type": "orders",
"links": { ... },
"attributes": { ... },
"relationships": { ... },
"meta": { ... }
},
"included": [
{
"id": "DvlGRmhdgX",
"type": "markets",
"links": { ... },
"attributes": { ... },
"relationships": { ... },
"meta": { ... }
},
{
"id": "kdPgtRXOKL",
"type": "line_items",
"links": { ... },
"attributes": { ... },
"relationships": { ... },
"meta": { ... }
},
{
"id": "XGZwpOSrWL",
"type": "skus",
"links": { ... },
"attributes": { ... },
"relationships": { ... },
"meta": { ... }
}
{
"id": "BgnguJvXmb",
"type": "addresses",
"links": { ... },
"attributes": { ... },
"relationships": { ... },
"meta": { ... }
},
{
"id": "AlrkugwyVW",
"type": "addresses",
"links": { ... },
"attributes": { ... },
"relationships": { ... },
"meta": { ... }
},
{
"id": "FdefrQxCba",
"type": "shipments",
"links": { ... },
"attributes": { ... },
"relationships": { ... },
"meta": { ... }
},
{
"id": "SfdyHtjfBF",
"type": "shipping_methods",
"links": { ... },
"attributes": { ... },
"relationships": { ... },
"meta": { ... }
},
{ ... }
]
}
{% hint style="warning" %}
In case the call to your external endpoint goes timeout, responds with an internal server error, or is blocked by the open [circuit breaker](https://docs.commercelayer.io/core/external-resources/..#circuit-breaker), the API keeps responding with a `200 OK` status code. No validation errors are attached to the order, but the `validations_count` value and the circuit breaker internal counter (if closed) are incremented.
{% endhint %}
{% hint style="danger" %}
The [override of the default list](https://docs.commercelayer.io/core/external-resources/..#custom-include-list) of included resources is not supported for external order validation.
{% endhint %}
### Response
Your service response (or error) must match the format described in the example below.
{% hint style="info" %}
Remember to pass the attribute-specific errors within the `data` object, associating them with the related order's attribute. If some error is not associated with any particular attribute use the `base` key (automatically filled with the error messages associated with any invalid attribute, if present).
{% endhint %}
#### Example
{% tabs %}
{% tab title="Response" %}
The successful response must be a JSON object, returning an empty body, meaning that the external logic running the validation has found no errors:
```json
{
"success": true,
"data": {}
}
```
{% endtab %}
{% tab title="Error" %}
On error, you must respond with an HTTP code >= `400`. The response body must be a JSON object containing the names of the order's attributes that generated the error(s) and one (a string) or more (an array) associated error message(s) as the value of the `data` key, plus any other relevant error code and message as the value of the `error` key:
```json
{
"success": false,
"data": {
"line_items": ["must be at least 3", "cannot weight more than 2000gr"],
"shipping_address": "is not recognized by our geo-location service",
"base": "standard error"
},
"error": {
"code": "YOUR-ERROR-CODE",
"message": "Your error message"
}
}
```
{% endtab %}
{% endtabs %}
### Security
When you activate external validation, a **shared secret** is generated at the market level. We recommend verifying the callback authenticity by signing the payload with that shared secret and comparing the result with the callback signature header.
{% content-ref url="../callbacks-security" %}
[callbacks-security](https://docs.commercelayer.io/core/callbacks-security)
{% endcontent-ref %}