curl --request POST \
  --url https://api.lemlist.com/api/campaigns/{campaignId}/senders \
  --header 'Authorization: Basic <encoded-value>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "senders": [
    {
      "userId": "usr_A1b2C3d4E5f6G7h8N"
    }
  ]
}
'

import requests

url = "https://api.lemlist.com/api/campaigns/{campaignId}/senders"

payload = { "senders": [{ "userId": "usr_A1b2C3d4E5f6G7h8N" }] }
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({senders: [{userId: 'usr_A1b2C3d4E5f6G7h8N'}]})
};

fetch('https://api.lemlist.com/api/campaigns/{campaignId}/senders', 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}/senders")

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  \"senders\": [\n    {\n      \"userId\": \"usr_A1b2C3d4E5f6G7h8N\"\n    }\n  ]\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}/senders",
  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([
    'senders' => [
        [
                'userId' => 'usr_A1b2C3d4E5f6G7h8N'
        ]
    ]
  ]),
  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;
}

{
  "data": {
    "campaignId": "cam_A1b2C3d4E5f6G7h8M",
    "senderStrategy": "random",
    "espMatching": false,
    "readOnly": false,
    "senders": [
      {
        "userId": "usr_A1b2C3d4E5f6G7h8K",
        "name": "John Doe",
        "email": "john@example.com",
        "channels": [
          {
            "type": "email",
            "id": "usm_A1b2C3d4E5f6G7h8L",
            "label": "john@example.com",
            "alias": "john@example.com",
            "esp": "google",
            "diagnostics": []
          }
        ],
        "diagnostics": []
      },
      {
        "userId": "usr_A1b2C3d4E5f6G7h8N",
        "name": "Jane Smith",
        "email": "jane@example.com",
        "channels": [
          {
            "type": "email",
            "id": "usm_A1b2C3d4E5f6G7h8P",
            "label": "jane@example.com",
            "alias": "jane@example.com",
            "esp": "microsoft",
            "diagnostics": []
          }
        ],
        "diagnostics": []
      }
    ],
    "diagnostics": []
  }
}

{
  "error": "No step of the campaign uses this channel type. Add a step of this type first",
  "code": "SENDER_CAMPAIGN_CHANNEL_TYPE_NOT_REQUIRED"
}

The authentication you supplied is incorrect

route is available starting emailPro plan

{
  "error": "Campaign not found",
  "code": "SENDER_CAMPAIGN_NOT_FOUND"
}

{
  "error": "Route bad method",
  "code": "ROUTE_BAD_METHOD"
}

{
  "error": "The campaign uses a dynamic sender strategy: the leads select the senders",
  "code": "SENDER_CAMPAIGN_DYNAMIC_STRATEGY"
}