curl --request PUT \
  --url https://api.kit.com/v4/subscribers/{id} \
  --header 'Content-Type: application/json' \
  --header 'X-Kit-Api-Key: <api-key>' \
  --data '
{
  "first_name": "Alice",
  "email_address": "alice@convertkit.dev",
  "fields": {
    "last_name": "Lamarr",
    "birthday": "Feb 17",
    "source": "landing page",
    "role": "Software developer",
    "company": "Convertkit",
    "postal_code": "83702",
    "website": "convertkit.com",
    "social_media": "https://www.linkedin.com/company/convertkit",
    "how_did_you_hear_about_us": "Social media",
    "interests": "Monetization",
    "coupon": ""
  }
}
'

require 'uri'
require 'net/http'

url = URI("https://api.kit.com/v4/subscribers/{id}")

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

request = Net::HTTP::Put.new(url)
request["X-Kit-Api-Key"] = '<api-key>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"first_name\": \"Alice\",\n  \"email_address\": \"alice@convertkit.dev\",\n  \"fields\": {\n    \"last_name\": \"Lamarr\",\n    \"birthday\": \"Feb 17\",\n    \"source\": \"landing page\",\n    \"role\": \"Software developer\",\n    \"company\": \"Convertkit\",\n    \"postal_code\": \"83702\",\n    \"website\": \"convertkit.com\",\n    \"social_media\": \"https://www.linkedin.com/company/convertkit\",\n    \"how_did_you_hear_about_us\": \"Social media\",\n    \"interests\": \"Monetization\",\n    \"coupon\": \"\"\n  }\n}"

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

const options = {
  method: 'PUT',
  headers: {'X-Kit-Api-Key': '<api-key>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    first_name: 'Alice',
    email_address: 'alice@convertkit.dev',
    fields: {
      last_name: 'Lamarr',
      birthday: 'Feb 17',
      source: 'landing page',
      role: 'Software developer',
      company: 'Convertkit',
      postal_code: '83702',
      website: 'convertkit.com',
      social_media: 'https://www.linkedin.com/company/convertkit',
      how_did_you_hear_about_us: 'Social media',
      interests: 'Monetization',
      coupon: ''
    }
  })
};

fetch('https://api.kit.com/v4/subscribers/{id}', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

package main

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

func main() {

	url := "https://api.kit.com/v4/subscribers/{id}"

	payload := strings.NewReader("{\n  \"first_name\": \"Alice\",\n  \"email_address\": \"alice@convertkit.dev\",\n  \"fields\": {\n    \"last_name\": \"Lamarr\",\n    \"birthday\": \"Feb 17\",\n    \"source\": \"landing page\",\n    \"role\": \"Software developer\",\n    \"company\": \"Convertkit\",\n    \"postal_code\": \"83702\",\n    \"website\": \"convertkit.com\",\n    \"social_media\": \"https://www.linkedin.com/company/convertkit\",\n    \"how_did_you_hear_about_us\": \"Social media\",\n    \"interests\": \"Monetization\",\n    \"coupon\": \"\"\n  }\n}")

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

	req.Header.Add("X-Kit-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))

}

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.kit.com/v4/subscribers/{id}",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "PUT",
  CURLOPT_POSTFIELDS => json_encode([
    'first_name' => 'Alice',
    'email_address' => 'alice@convertkit.dev',
    'fields' => [
        'last_name' => 'Lamarr',
        'birthday' => 'Feb 17',
        'source' => 'landing page',
        'role' => 'Software developer',
        'company' => 'Convertkit',
        'postal_code' => '83702',
        'website' => 'convertkit.com',
        'social_media' => 'https://www.linkedin.com/company/convertkit',
        'how_did_you_hear_about_us' => 'Social media',
        'interests' => 'Monetization',
        'coupon' => ''
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json",
    "X-Kit-Api-Key: <api-key>"
  ],
]);

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

curl_close($curl);

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

import requests

url = "https://api.kit.com/v4/subscribers/{id}"

payload = {
    "first_name": "Alice",
    "email_address": "alice@convertkit.dev",
    "fields": {
        "last_name": "Lamarr",
        "birthday": "Feb 17",
        "source": "landing page",
        "role": "Software developer",
        "company": "Convertkit",
        "postal_code": "83702",
        "website": "convertkit.com",
        "social_media": "https://www.linkedin.com/company/convertkit",
        "how_did_you_hear_about_us": "Social media",
        "interests": "Monetization",
        "coupon": ""
    }
}
headers = {
    "X-Kit-Api-Key": "<api-key>",
    "Content-Type": "application/json"
}

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

print(response.text)

{
  "subscriber": {
    "id": 378,
    "first_name": "Alice",
    "email_address": "alice@convertkit.dev",
    "state": "active",
    "created_at": "2023-02-17T11:43:55Z",
    "fields": {
      "birthday": "Feb 17",
      "last_name": "Lamarr",
      "source": "landing page"
    }
  }
}

{
  "subscriber": {
    "id": 380,
    "first_name": "Alice",
    "email_address": "alice@convertkit.dev",
    "state": "active",
    "created_at": "2023-02-17T11:43:55Z",
    "fields": {
      "birthday": null,
      "company": null,
      "coupon": null,
      "how_did_you_hear_about_us": null,
      "interests": null,
      "last_name": null,
      "postal_code": null,
      "role": null,
      "social_media": null,
      "source": null,
      "website": null
    }
  }
}

{
  "errors": [
    "The access token is invalid"
  ]
}

{
  "errors": [
    "Not Found"
  ]
}

{
  "errors": [
    "Email address has already been taken"
  ]
}