> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.mercoa.com/embedded-ap-ar/api-reference/entity/external-accounting-system/create/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.mercoa.com/_mcp/server.

# Create/Update External Entity

POST https://api.mercoa.com/entity/{entityId}/external-accounting-system/create
Content-Type: application/json

Create/Link an entity to an external accounting system like Codat or Rutter. If the entity is already linked to an external accounting system, this will return the existing connection.

Reference: https://docs.mercoa.com/embedded-ap-ar/api-reference/entity/external-accounting-system/create

## Authentication

- `Authorization` header (bearer token, required) — Bearer authentication of the form `Bearer <token>`, where token is your auth token.

## Request

### Path parameters

- `entityId` (string, required) — Entity ID or Entity ForeignID

### Body (application/json)

This endpoint expects an object.

- `object`
  - `type`: `codat`
    - `companyId` (string, optional) — If the company already exists in Codat, provide the company ID to link the company to the entity. If the company does not exist, leave this field blank and Codat will create a new company.
  - `type`: `rutter`
    - `accessToken` (string, optional) — The access token for the existing Rutter connection. If the connection does not exist, leave this field blank and Rutter will create a new connection.

## Response

### 200

- `object`
  - `type`: `codat`
    - `companyId` (string, required)
  - `type`: `rutter`
    - `accessToken` (string, required)
  - `type`: `none`
    - `companyId` (string, required)

## Errors

### 400 Bad Request

- `errorName` ("BadRequest", required)
- `content` (string, required)

### 401 Unauthorized

- `errorName` ("Unauthorized", required)
- `content` (string, required)

### 403 Forbidden

- `errorName` ("Forbidden", required)
- `content` (string, required)

### 404 Not Found

- `errorName` ("NotFound", required)
- `content` (string, required)

### 409 Conflict

- `errorName` ("Conflict", required)
- `content` (string, required)

### 500 Internal Server Error

- `errorName` ("InternalServerError", required)
- `content` (string, required)

### 501 Unimplemented

- `errorName` ("Unimplemented", required)
- `content` (string, required)

## Examples

**Request**

```json
{
  "type": "rutter",
  "accessToken": "123"
}
```

**Response**

```json
{
  "type": "rutter",
  "accessToken": "123"
}
```

**SDK Code**

```python Default
import requests

url = "https://api.mercoa.com/entity/ent_8545a84e-a45f-41bf-bdf1-33b42a55812c/external-accounting-system/create"

payload = {
    "type": "rutter",
    "accessToken": "123"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

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

print(response.json())
```

```typescript Default
import { MercoaClient } from "@mercoa/javascript";

const client = new MercoaClient({ token: "YOUR_TOKEN" });
await client.entity.externalAccountingSystem.create("ent_8545a84e-a45f-41bf-bdf1-33b42a55812c", {
    type: "rutter",
    accessToken: "123"
});

```

```go Default
package main

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

func main() {

	url := "https://api.mercoa.com/entity/ent_8545a84e-a45f-41bf-bdf1-33b42a55812c/external-accounting-system/create"

	payload := strings.NewReader("{\n  \"type\": \"rutter\",\n  \"accessToken\": \"123\"\n}")

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

	req.Header.Add("Authorization", "Bearer <token>")
	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 Default
require 'uri'
require 'net/http'

url = URI("https://api.mercoa.com/entity/ent_8545a84e-a45f-41bf-bdf1-33b42a55812c/external-accounting-system/create")

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

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"type\": \"rutter\",\n  \"accessToken\": \"123\"\n}"

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

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

HttpResponse<String> response = Unirest.post("https://api.mercoa.com/entity/ent_8545a84e-a45f-41bf-bdf1-33b42a55812c/external-accounting-system/create")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"type\": \"rutter\",\n  \"accessToken\": \"123\"\n}")
  .asString();
```

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

$client = new \GuzzleHttp\Client();

$response = $client->request('POST', 'https://api.mercoa.com/entity/ent_8545a84e-a45f-41bf-bdf1-33b42a55812c/external-accounting-system/create', [
  'body' => '{
  "type": "rutter",
  "accessToken": "123"
}',
  'headers' => [
    'Authorization' => 'Bearer <token>',
    'Content-Type' => 'application/json',
  ],
]);

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

```csharp Default
using RestSharp;

var client = new RestClient("https://api.mercoa.com/entity/ent_8545a84e-a45f-41bf-bdf1-33b42a55812c/external-accounting-system/create");
var request = new RestRequest(Method.POST);
request.AddHeader("Authorization", "Bearer <token>");
request.AddHeader("Content-Type", "application/json");
request.AddParameter("application/json", "{\n  \"type\": \"rutter\",\n  \"accessToken\": \"123\"\n}", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
```

```swift Default
import Foundation

let headers = [
  "Authorization": "Bearer <token>",
  "Content-Type": "application/json"
]
let parameters = [
  "type": "rutter",
  "accessToken": "123"
] as [String : Any]

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

let request = NSMutableURLRequest(url: NSURL(string: "https://api.mercoa.com/entity/ent_8545a84e-a45f-41bf-bdf1-33b42a55812c/external-accounting-system/create")! 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()
```