Create a side letter.

curl -X POST "https://api.mattermode.com/v1/entities/{id}/side_letters" \  -H "Content-Type: application/json" \  -d '{    "parent": {      "kind": "convertible",      "id": "string"    },    "investor_stakeholder_id": "string",    "clauses": [      {}    ]  }'

const body = JSON.stringify({  "parent": {    "kind": "convertible",    "id": "string"  },  "investor_stakeholder_id": "string",  "clauses": [    {}  ]})fetch("https://api.mattermode.com/v1/entities/{id}/side_letters", {  method: "POST",  headers: {    "Content-Type": "application/json"  },  body})

package mainimport (  "fmt"  "net/http"  "io/ioutil"  "strings")func main() {  url := "https://api.mattermode.com/v1/entities/{id}/side_letters"  body := strings.NewReader(`{    "parent": {      "kind": "convertible",      "id": "string"    },    "investor_stakeholder_id": "string",    "clauses": [      {}    ]  }`)  req, _ := http.NewRequest("POST", url, body)  req.Header.Add("Content-Type", "application/json")  res, _ := http.DefaultClient.Do(req)  defer res.Body.Close()  body, _ := ioutil.ReadAll(res.Body)  fmt.Println(res)  fmt.Println(string(body))}

import requestsheaders = {    "Authorization": "Bearer sk_test_4eC39HqLyjWDarjtT1zdp7dc",    "Matter-Version": "2026-06-10",    "Idempotency-Key": "ee7c3a9b-3f1a-4d8e-9b2a-7c5e1f0a2d4b",}payload = {    "parent": {        "kind": "convertible",        "id": "example"    },    "investor_stakeholder_id": "example",    "clauses": [        {}    ]}resp = requests.post(    "https://api.mattermode.com/v1/entities/ent_Nq3KcAbc/side_letters",    headers=headers,    json=payload,)resp.raise_for_status()print(resp.json())

import java.net.URI;import java.net.http.HttpClient;import java.net.http.HttpRequest;import java.net.http.HttpResponse;import java.net.http.HttpResponse.BodyHandlers;import java.time.Duration;import java.net.http.HttpRequest.BodyPublishers;var body = BodyPublishers.ofString("""{  "parent": {    "kind": "convertible",    "id": "string"  },  "investor_stakeholder_id": "string",  "clauses": [    {}  ]}""");HttpClient client = HttpClient.newBuilder()  .connectTimeout(Duration.ofSeconds(10))  .build();HttpRequest.Builder requestBuilder = HttpRequest.newBuilder()  .uri(URI.create("https://api.mattermode.com/v1/entities/{id}/side_letters"))  .header("Content-Type", "application/json")  .POST(body)  .build();try {  HttpResponse<String> response = client.send(requestBuilder.build(), BodyHandlers.ofString());  System.out.println("Status code: " + response.statusCode());  System.out.println("Response body: " + response.body());} catch (Exception e) {  e.printStackTrace();}

using System;using System.Net.Http;using System.Text;var body = new StringContent("""{  "parent": {    "kind": "convertible",    "id": "string"  },  "investor_stakeholder_id": "string",  "clauses": [    {}  ]}""", Encoding.UTF8, "application/json");var client = new HttpClient();var response = await client.PostAsync("https://api.mattermode.com/v1/entities/{id}/side_letters", body);var responseBody = await response.Content.ReadAsStringAsync();

curl --request POST 'https://api.mattermode.com/v1/entities/ent_Nq3KcAbc/side_letters' \  --header 'Authorization: Bearer sk_test_4eC39HqLyjWDarjtT1zdp7dc' \  --header 'Matter-Version: 2026-06-10' \  --header 'Idempotency-Key: ee7c3a9b-3f1a-4d8e-9b2a-7c5e1f0a2d4b' \  --header 'Content-Type: application/json' \  --data '{  "parent": {    "kind": "convertible",    "id": "example"  },  "investor_stakeholder_id": "example",  "clauses": [    {}  ]}'

const response = await fetch("https://api.mattermode.com/v1/entities/ent_Nq3KcAbc/side_letters", {  method: "POST",  headers: {    "Authorization": "Bearer sk_test_4eC39HqLyjWDarjtT1zdp7dc",    "Matter-Version": "2026-06-10",    "Idempotency-Key": "ee7c3a9b-3f1a-4d8e-9b2a-7c5e1f0a2d4b",    "Content-Type": "application/json",  },  body: JSON.stringify({    "parent": {      "kind": "convertible",      "id": "example"    },    "investor_stakeholder_id": "example",    "clauses": [      {}    ]  }),});if (!response.ok) {  throw new Error(`Matter API ${response.status}: ${await response.text()}`);}const data = await response.json();console.log(data);