curl --request PATCH \
  --url https://api.assembly.com/v1/custom-fields/{id} \
  --header 'Content-Type: application/json' \
  --header 'X-API-KEY: <api-key>' \
  --data '
{
  "entityType": "client",
  "name": "Account tier",
  "options": [
    {
      "label": "High priority",
      "id": "option-f1a2b3c4-d5e6-47a8-9b0c-1d2e3f4a5b6c"
    }
  ],
  "type": "multiSelect"
}
'

import requests

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

payload = {
    "entityType": "client",
    "name": "Account tier",
    "options": [
        {
            "label": "High priority",
            "id": "option-f1a2b3c4-d5e6-47a8-9b0c-1d2e3f4a5b6c"
        }
    ],
    "type": "multiSelect"
}
headers = {
    "X-API-KEY": "<api-key>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'PATCH',
  headers: {'X-API-KEY': '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    entityType: 'client',
    name: 'Account tier',
    options: [{label: 'High priority', id: 'option-f1a2b3c4-d5e6-47a8-9b0c-1d2e3f4a5b6c'}],
    type: 'multiSelect'
  })
};

fetch('https://api.assembly.com/v1/custom-fields/{id}', 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/{id}",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "PATCH",
  CURLOPT_POSTFIELDS => json_encode([
    'entityType' => 'client',
    'name' => 'Account tier',
    'options' => [
        [
                'label' => 'High priority',
                'id' => 'option-f1a2b3c4-d5e6-47a8-9b0c-1d2e3f4a5b6c'
        ]
    ],
    'type' => 'multiSelect'
  ]),
  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/{id}"

	payload := strings.NewReader("{\n  \"entityType\": \"client\",\n  \"name\": \"Account tier\",\n  \"options\": [\n    {\n      \"label\": \"High priority\",\n      \"id\": \"option-f1a2b3c4-d5e6-47a8-9b0c-1d2e3f4a5b6c\"\n    }\n  ],\n  \"type\": \"multiSelect\"\n}")

	req, _ := http.NewRequest("PATCH", 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.patch("https://api.assembly.com/v1/custom-fields/{id}")
  .header("X-API-KEY", "<api-key>")
  .header("Content-Type", "application/json")
  .body("{\n  \"entityType\": \"client\",\n  \"name\": \"Account tier\",\n  \"options\": [\n    {\n      \"label\": \"High priority\",\n      \"id\": \"option-f1a2b3c4-d5e6-47a8-9b0c-1d2e3f4a5b6c\"\n    }\n  ],\n  \"type\": \"multiSelect\"\n}")
  .asString();

require 'uri'
require 'net/http'

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

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

request = Net::HTTP::Patch.new(url)
request["X-API-KEY"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"entityType\": \"client\",\n  \"name\": \"Account tier\",\n  \"options\": [\n    {\n      \"label\": \"High priority\",\n      \"id\": \"option-f1a2b3c4-d5e6-47a8-9b0c-1d2e3f4a5b6c\"\n    }\n  ],\n  \"type\": \"multiSelect\"\n}"

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

{
  "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>"
}

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