> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.withverifa.com/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.withverifa.com/_mcp/server.

# Create an identity relationship

POST https://api.withverifa.com/api/v1/identities/{identity_id}/relationships
Content-Type: application/json

Creates a bidirectional relationship between two identities. Accepts
either a built-in user type or the `name` of an active custom
relationship type defined via `/relationship-types`. System relationship
types (`same_document`, `same_name_dob`, `same_ssn`, `merged`, etc.)
cannot be created via the API.


Reference: https://docs.withverifa.com/api-reference/identities/create-identity-relationship

## Authentication

- `X-API-Key` header (required) — Organization API key. Keys are prefixed with `vk_live_` (production) or `vk_sandbox_` (sandbox).

## Request

### Path parameters

- `identity_id` (string, required) — Identity ID (`idn_*`) or external reference.

### Headers

- `Verifa-Version` (date, optional) — API version date string (e.g. `2026-02-01`). If omitted, the version pinned to your API key is used.
- `Key-Inflection` (enum, optional, default: snake) — Response key casing. Defaults to `snake`.
  - Allowed values: `camel`, `kebab`, `snake`
- `Idempotency-Key` (string, optional) — Unique key for idempotent requests. Cached for 24 hours. Sending the same key with different parameters returns `422`.

### Body (application/json)

This endpoint expects an object.

- `related_identity_id` (string, required) — The identity to link to.
- `relationship_type` (string, optional, default: user_linked) — Built-in user type (`user_linked`, `same_household`, `family_member`, `business_associate`, `authorized_representative`, `power_of_attorney`, `beneficial_owner`, `related_account`) or the `name` of an active custom relationship type.
- `note` (string, optional) — Optional note explaining the reason for linking.
- `metadata` (map from string to any, optional) — Optional metadata to attach to the relationship.

## Response

### 201

Relationship created.

- `id` (string, required)
- `source_identity_id` (string, required)
- `related_identity_id` (string, required)
- `relationship_type` (string, required)
- `metadata` (ApiV1IdentitiesIdentityIdRelationshipsPostResponsesContentApplicationJsonSchemaMetadata, required)

## Errors

### 401 Unauthorized Error

Missing or invalid API key.

- `error` (string, required) — Short error code.
- `status_code` (integer, required) — HTTP status code.
- `detail` (string, optional) — Human-readable error description.

### 404 Not Found Error

Resource not found.

- `error` (string, required) — Short error code.
- `status_code` (integer, required) — HTTP status code.
- `detail` (string, optional) — Human-readable error description.

### 422 Unprocessable Entity Error

Validation error (system type, self-link, or related identity not found).

- `error` (string, required) — Short error code.
- `status_code` (integer, required) — HTTP status code.
- `detail` (string, optional) — Human-readable error description.

## Types

### ApiV1IdentitiesIdentityIdRelationshipsPostResponsesContentApplicationJsonSchemaMetadata

## Examples

**Request**

```json
{
  "related_identity_id": "idn_def456"
}
```

**Response**

```json
{
  "id": "idrel_abc123",
  "source_identity_id": "idn_abc123",
  "related_identity_id": "idn_def456",
  "relationship_type": "user_linked",
  "metadata": {}
}
```

**SDK Code**

```python
import requests

url = "https://api.withverifa.com/api/v1/identities/identity_id/relationships"

payload = { "related_identity_id": "idn_def456" }
headers = {
    "X-API-Key": "<apiKey>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.json())
```

```javascript
const url = 'https://api.withverifa.com/api/v1/identities/identity_id/relationships';
const options = {
  method: 'POST',
  headers: {'X-API-Key': '<apiKey>', 'Content-Type': 'application/json'},
  body: '{"related_identity_id":"idn_def456"}'
};

try {
  const response = await fetch(url, options);
  const data = await response.json();
  console.log(data);
} catch (error) {
  console.error(error);
}
```

```go
package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://api.withverifa.com/api/v1/identities/identity_id/relationships"

	payload := strings.NewReader("{\n  \"related_identity_id\": \"idn_def456\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("X-API-Key", "<apiKey>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(res)
	fmt.Println(string(body))

}
```

```ruby
require 'uri'
require 'net/http'

url = URI("https://api.withverifa.com/api/v1/identities/identity_id/relationships")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["X-API-Key"] = '<apiKey>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"related_identity_id\": \"idn_def456\"\n}"

response = http.request(request)
puts response.read_body
```

```java
import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;

HttpResponse<String> response = Unirest.post("https://api.withverifa.com/api/v1/identities/identity_id/relationships")
  .header("X-API-Key", "<apiKey>")
  .header("Content-Type", "application/json")
  .body("{\n  \"related_identity_id\": \"idn_def456\"\n}")
  .asString();
```

```php
<?php
require_once('vendor/autoload.php');

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.withverifa.com/api/v1/identities/identity_id/relationships', [
  'body' => '{
  "related_identity_id": "idn_def456"
}',
  'headers' => [
    'Content-Type' => 'application/json',
    'X-API-Key' => '<apiKey>',
  ],
]);

echo $response->getBody();
```

```csharp
using RestSharp;

var client = new RestClient("https://api.withverifa.com/api/v1/identities/identity_id/relationships");
var request = new RestRequest(Method.POST);
request.AddHeader("X-API-Key", "<apiKey>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"related_identity_id\": \"idn_def456\"\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift
import Foundation

let headers = [
  "X-API-Key": "<apiKey>",
  "Content-Type": "application/json"
]
let parameters = ["related_identity_id": "idn_def456"] as [String : Any]

let postData = JSONSerialization.data(withJSONObject: parameters, options: [])

let request = NSMutableURLRequest(url: NSURL(string: "https://api.withverifa.com/api/v1/identities/identity_id/relationships")! as URL,
                                        cachePolicy: .useProtocolCachePolicy,
                                    timeoutInterval: 10.0)
request.httpMethod = "POST"
request.allHTTPHeaderFields = headers
request.httpBody = postData as Data

let session = URLSession.shared
let dataTask = session.dataTask(with: request as URLRequest, completionHandler: { (data, response, error) -> Void in
  if (error != nil) {
    print(error as Any)
  } else {
    let httpResponse = response as? HTTPURLResponse
    print(httpResponse)
  }
})

dataTask.resume()
```