curl --request POST \
  --url https://api.notion.com/admin/v1/legal_holds/{legal_hold_id}/users \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'Notion-Version: <notion-version>' \
  --data '
{
  "user_ids": [
    "3c90c3cc-0d44-4b50-8888-8dd25736052a"
  ]
}
'

import requests

url = "https://api.notion.com/admin/v1/legal_holds/{legal_hold_id}/users"

payload = { "user_ids": ["3c90c3cc-0d44-4b50-8888-8dd25736052a"] }
headers = {
    "Notion-Version": "<notion-version>",
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {
    'Notion-Version': '<notion-version>',
    Authorization: 'Bearer <token>',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({user_ids: ['3c90c3cc-0d44-4b50-8888-8dd25736052a']})
};

fetch('https://api.notion.com/admin/v1/legal_holds/{legal_hold_id}/users', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.notion.com/admin/v1/legal_holds/{legal_hold_id}/users",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'user_ids' => [
        '3c90c3cc-0d44-4b50-8888-8dd25736052a'
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json",
    "Notion-Version: <notion-version>"
  ],
]);

$response = curl_exec($curl);
$err = curl_error($curl);

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

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

func main() {

	url := "https://api.notion.com/admin/v1/legal_holds/{legal_hold_id}/users"

	payload := strings.NewReader("{\n  \"user_ids\": [\n    \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n  ]\n}")

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

	req.Header.Add("Notion-Version", "<notion-version>")
	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(string(body))

}

HttpResponse<String> response = Unirest.post("https://api.notion.com/admin/v1/legal_holds/{legal_hold_id}/users")
  .header("Notion-Version", "<notion-version>")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"user_ids\": [\n    \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n  ]\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.notion.com/admin/v1/legal_holds/{legal_hold_id}/users")

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

request = Net::HTTP::Post.new(url)
request["Notion-Version"] = '<notion-version>'
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"user_ids\": [\n    \"3c90c3cc-0d44-4b50-8888-8dd25736052a\"\n  ]\n}"

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

{
  "created_by": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "created_time": 123,
  "id": "<string>",
  "start_date": 123,
  "user_interaction_type": [],
  "users": {
    "ids": [
      "3c90c3cc-0d44-4b50-8888-8dd25736052a"
    ],
    "total": 123
  },
  "workspaces": {
    "ids": [
      "3c90c3cc-0d44-4b50-8888-8dd25736052a"
    ],
    "total": 123
  },
  "description": "<string>",
  "end_date": 123,
  "icon": "<string>",
  "name": "<string>"
}

{
  "type": "error",
  "code": "validation_error",
  "status": 400,
  "message": "The request body is invalid."
}

{
  "type": "error",
  "code": "unauthorized",
  "status": 401,
  "message": "Unauthorized."
}

{
  "type": "error",
  "code": "forbidden",
  "status": 403,
  "message": "Forbidden."
}

{
  "type": "error",
  "code": "not_found",
  "status": 404,
  "message": "Not found."
}

{
  "type": "error",
  "code": "rate_limited",
  "status": 429,
  "message": "Rate limited."
}

{
  "type": "error",
  "code": "internal_server_error",
  "status": 500,
  "message": "An unexpected error occurred."
}