curl --request POST \
  --url https://api.lemlist.com/api/tasks \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "recordId": "ctc_ZpFy8SXl51PsctTGf",
  "type": "phone",
  "assignedTo": "usr_6nVZY7je1zSBXZgZK",
  "dueDate": "2025-02-10T09:58:57.169Z"
}
'

import requests

url = "https://api.lemlist.com/api/tasks"

payload = {
    "recordId": "ctc_ZpFy8SXl51PsctTGf",
    "type": "phone",
    "assignedTo": "usr_6nVZY7je1zSBXZgZK",
    "dueDate": "2025-02-10T09:58:57.169Z"
}
headers = {
    "Authorization": "Basic <encoded-value>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: 'Basic <encoded-value>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    recordId: 'ctc_ZpFy8SXl51PsctTGf',
    type: 'phone',
    assignedTo: 'usr_6nVZY7je1zSBXZgZK',
    dueDate: '2025-02-10T09:58:57.169Z'
  })
};

fetch('https://api.lemlist.com/api/tasks', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

require 'uri'
require 'net/http'

url = URI("https://api.lemlist.com/api/tasks")

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

request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Basic <encoded-value>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"recordId\": \"ctc_ZpFy8SXl51PsctTGf\",\n  \"type\": \"phone\",\n  \"assignedTo\": \"usr_6nVZY7je1zSBXZgZK\",\n  \"dueDate\": \"2025-02-10T09:58:57.169Z\"\n}"

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

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.lemlist.com/api/tasks",
  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([
    'recordId' => 'ctc_ZpFy8SXl51PsctTGf',
    'type' => 'phone',
    'assignedTo' => 'usr_6nVZY7je1zSBXZgZK',
    'dueDate' => '2025-02-10T09:58:57.169Z'
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Basic <encoded-value>",
    "Content-Type: application/json"
  ],
]);

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

curl_close($curl);

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

{
  "_id": "opp_LyXDV8KHzctQdLFpG",
  "type": "manual",
  "title": "Keep an eye on him",
  "priority": 1,
  "leadId": "lea_fiDpiGV585wy3Oii2",
  "campaignId": "cam_bSn8EORHQxbWPjHvu",
  "contactId": "ctc_xW8Ou6C03Csv8vatp",
  "dueDate": "2025-11-10T09:58:57.169Z",
  "userId": "usr_ahfFktBBHUIxbVG5P",
  "content": "does he have bandwidth to help us? would be grand"
}

{
  "error": "recordId is required"
}

The authentication you supplied is incorrect