curl --request POST \
  --url https://api.assembly.com/v1/custom-fields \
  --header 'Content-Type: application/json' \
  --header 'X-API-KEY: <api-key>' \
  --data '
{
  "customFields": [
    {
      "entityType": "client",
      "name": "Account tier",
      "type": "multiSelect",
      "options": [
        {
          "label": "High priority"
        }
      ]
    }
  ]
}
'

import requests

url = "https://api.assembly.com/v1/custom-fields"

payload = { "customFields": [
        {
            "entityType": "client",
            "name": "Account tier",
            "type": "multiSelect",
            "options": [{ "label": "High priority" }]
        }
    ] }
headers = {
    "X-API-KEY": "<api-key>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {'X-API-KEY': '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    customFields: [
      {
        entityType: 'client',
        name: 'Account tier',
        type: 'multiSelect',
        options: [{label: 'High priority'}]
      }
    ]
  })
};

fetch('https://api.assembly.com/v1/custom-fields', 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.assembly.com/v1/custom-fields",
  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([
    'customFields' => [
        [
                'entityType' => 'client',
                'name' => 'Account tier',
                'type' => 'multiSelect',
                'options' => [
                                [
                                                                'label' => 'High priority'
                                ]
                ]
        ]
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json",
    "X-API-KEY: <api-key>"
  ],
]);

$response = curl_exec($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.assembly.com/v1/custom-fields"

	payload := strings.NewReader("{\n  \"customFields\": [\n    {\n      \"entityType\": \"client\",\n      \"name\": \"Account tier\",\n      \"type\": \"multiSelect\",\n      \"options\": [\n        {\n          \"label\": \"High priority\"\n        }\n      ]\n    }\n  ]\n}")

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

	req.Header.Add("X-API-KEY", "<api-key>")
	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.assembly.com/v1/custom-fields")
  .header("X-API-KEY", "<api-key>")
  .header("Content-Type", "application/json")
  .body("{\n  \"customFields\": [\n    {\n      \"entityType\": \"client\",\n      \"name\": \"Account tier\",\n      \"type\": \"multiSelect\",\n      \"options\": [\n        {\n          \"label\": \"High priority\"\n        }\n      ]\n    }\n  ]\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://api.assembly.com/v1/custom-fields")

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

request = Net::HTTP::Post.new(url)
request["X-API-KEY"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"customFields\": [\n    {\n      \"entityType\": \"client\",\n      \"name\": \"Account tier\",\n      \"type\": \"multiSelect\",\n      \"options\": [\n        {\n          \"label\": \"High priority\"\n        }\n      ]\n    }\n  ]\n}"

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

{
  "customFields": [
    {
      "entityType": "client",
      "id": "d8e8fca2-dc0f-4f3b-9a2e-1f6f3c2b7a10",
      "key": "accountTier",
      "name": "Account tier",
      "object": "customField",
      "options": [
        {
          "color": "rgba(204, 0, 0, 1)",
          "id": "f1a2b3c4-d5e6-47a8-9b0c-1d2e3f4a5b6c",
          "key": "highPriority",
          "label": "High priority",
          "object": "customFieldOption"
        }
      ],
      "order": 0,
      "type": "multiSelect"
    }
  ]
}

{
  "code": "<string>",
  "data": "<unknown>",
  "message": "<string>"
}

{
  "code": "<string>",
  "data": "<unknown>",
  "message": "<string>"
}

{
  "code": "<string>",
  "data": "<unknown>",
  "message": "<string>"
}