curl --request PUT \
  --url https://api.lemlist.com/api/campaigns/{campaignId}/leads/{leadIdOrEmail}/steps/{stepId}/personalization \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "message": "<p>Hi {{firstName}}, a quick follow-up on my last email.</p>"
}
'

import requests

url = "https://api.lemlist.com/api/campaigns/{campaignId}/leads/{leadIdOrEmail}/steps/{stepId}/personalization"

payload = { "message": "<p>Hi {{firstName}}, a quick follow-up on my last email.</p>" }
headers = {
    "Authorization": "Basic <encoded-value>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'PUT',
  headers: {Authorization: 'Basic <encoded-value>', 'Content-Type': 'application/json'},
  body: JSON.stringify({message: '<p>Hi {{firstName}}, a quick follow-up on my last email.</p>'})
};

fetch('https://api.lemlist.com/api/campaigns/{campaignId}/leads/{leadIdOrEmail}/steps/{stepId}/personalization', 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/campaigns/{campaignId}/leads/{leadIdOrEmail}/steps/{stepId}/personalization")

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

request = Net::HTTP::Put.new(url)
request["Authorization"] = 'Basic <encoded-value>'
request["Content-Type"] = 'application/json'
request.body = "{\n  \"message\": \"<p>Hi {{firstName}}, a quick follow-up on my last email.</p>\"\n}"

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

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.lemlist.com/api/campaigns/{campaignId}/leads/{leadIdOrEmail}/steps/{stepId}/personalization",
  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([
    'message' => '<p>Hi {{firstName}}, a quick follow-up on my last email.</p>'
  ]),
  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;
}

{
  "leadId": "lea_Example6F7g8H9i0J",
  "stepId": "stp_Example1K2l3M4n5O",
  "variant": "A",
  "emailTemplateId": "etp_Example6P7q8R9s0T",
  "content": {
    "subject": "",
    "message": "<p>Hi {{firstName}}, a quick follow-up on my last email.</p>",
    "cc": [
      "jane@example.com"
    ]
  }
}

{
  "error": "Validation error",
  "code": "VALIDATION_ERROR"
}

"The authentication you supplied is incorrect"

{
  "error": "Lead not found in this campaign",
  "code": "REVIEW_DRAFT_LEAD_NOT_FOUND"
}

{
  "error": "The lead already reached this step: its message can no longer be personalized",
  "code": "REVIEW_DRAFT_STEP_ALREADY_REACHED"
}

{
  "error": "This A/B variant is not available on the step (no variant B, or the other variant won)",
  "code": "REVIEW_DRAFT_VARIANT_UNAVAILABLE"
}