curl --request POST \
  --url https://api.itmc.i.moneyforward.com/api/v1/organizations/{organizationId}/identity/fields/custom \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "kind": "dropdown",
  "configuration": {
    "values": [
      {
        "id": "option_1",
        "value": "Option 1",
        "group": "<string>"
      }
    ]
  },
  "attributeName": "foo bar",
  "attributeCode": "employee_id"
}
'

import requests

url = "https://api.itmc.i.moneyforward.com/api/v1/organizations/{organizationId}/identity/fields/custom"

payload = {
    "kind": "dropdown",
    "configuration": { "values": [
            {
                "id": "option_1",
                "value": "Option 1",
                "group": "<string>"
            }
        ] },
    "attributeName": "foo bar",
    "attributeCode": "employee_id"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    kind: 'dropdown',
    configuration: {values: [{id: 'option_1', value: 'Option 1', group: '<string>'}]},
    attributeName: 'foo bar',
    attributeCode: 'employee_id'
  })
};

fetch('https://api.itmc.i.moneyforward.com/api/v1/organizations/{organizationId}/identity/fields/custom', 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.itmc.i.moneyforward.com/api/v1/organizations/{organizationId}/identity/fields/custom",
  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([
    'kind' => 'dropdown',
    'configuration' => [
        'values' => [
                [
                                'id' => 'option_1',
                                'value' => 'Option 1',
                                'group' => '<string>'
                ]
        ]
    ],
    'attributeName' => 'foo bar',
    'attributeCode' => 'employee_id'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json"
  ],
]);

$response = curl_exec($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.itmc.i.moneyforward.com/api/v1/organizations/{organizationId}/identity/fields/custom"

	payload := strings.NewReader("{\n  \"kind\": \"dropdown\",\n  \"configuration\": {\n    \"values\": [\n      {\n        \"id\": \"option_1\",\n        \"value\": \"Option 1\",\n        \"group\": \"<string>\"\n      }\n    ]\n  },\n  \"attributeName\": \"foo bar\",\n  \"attributeCode\": \"employee_id\"\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(string(body))

}

HttpResponse<String> response = Unirest.post("https://api.itmc.i.moneyforward.com/api/v1/organizations/{organizationId}/identity/fields/custom")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"kind\": \"dropdown\",\n  \"configuration\": {\n    \"values\": [\n      {\n        \"id\": \"option_1\",\n        \"value\": \"Option 1\",\n        \"group\": \"<string>\"\n      }\n    ]\n  },\n  \"attributeName\": \"foo bar\",\n  \"attributeCode\": \"employee_id\"\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.itmc.i.moneyforward.com/api/v1/organizations/{organizationId}/identity/fields/custom")

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  \"kind\": \"dropdown\",\n  \"configuration\": {\n    \"values\": [\n      {\n        \"id\": \"option_1\",\n        \"value\": \"Option 1\",\n        \"group\": \"<string>\"\n      }\n    ]\n  },\n  \"attributeName\": \"foo bar\",\n  \"attributeCode\": \"employee_id\"\n}"

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

{
  "id": 1,
  "uniqueName": "custom_text_field",
  "name": "Foo bar",
  "kind": "dropdown",
  "serviceSource": {
    "workspaceId": 1,
    "serviceFieldId": "smarthr_city"
  },
  "serviceDetails": {
    "id": 33,
    "name": "SmartHR",
    "uniqueName": "smarthr",
    "serviceTopUrl": "https://smarthr.jp/"
  },
  "configuration": {
    "values": [
      {
        "id": "option_1",
        "value": "Option 1",
        "group": "<string>",
        "label": {
          "ja": "こんにちは",
          "en": "Hello"
        }
      }
    ],
    "groups": [
      {
        "value": "phone",
        "label": {
          "ja": "こんにちは",
          "en": "Hello"
        }
      }
    ]
  },
  "required": true
}