curl -X POST \
 /billing-groups \
 --header "Content-Type: application/json" \
 --header "Authorization: Bearer <token>" \
 --data '{
    "customer": "ad3f4b3c-1b2a-4d5c-8e6f-7a8b9c0d1e2f",
    "name": "Billing of payments at the end of the month",
    "type": "end_of_month",
    "customDay": "31",
    "customMonth": "12"
}'

import requests

url = "https://coreapi.io/billing-groups"

payload = {
    "customer": "ad3f4b3c-1b2a-4d5c-8e6f-7a8b9c0d1e2f",
    "name": "Billing of payments at the end of the month",
    "type": "end_of_month",
    "customDay": 31,
    "customMonth": 12
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

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

print(response.text)

const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    customer: 'ad3f4b3c-1b2a-4d5c-8e6f-7a8b9c0d1e2f',
    name: 'Billing of payments at the end of the month',
    type: 'end_of_month',
    customDay: 31,
    customMonth: 12
  })
};

fetch('https://coreapi.io/billing-groups', 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://coreapi.io/billing-groups",
  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([
    'customer' => 'ad3f4b3c-1b2a-4d5c-8e6f-7a8b9c0d1e2f',
    'name' => 'Billing of payments at the end of the month',
    'type' => 'end_of_month',
    'customDay' => 31,
    'customMonth' => 12
  ]),
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer <token>",
    "Content-Type: application/json"
  ],
]);

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

curl_close($curl);

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

{
  "name": "Billing of payments at the end of the month",
  "type": "end_of_month",
  "id": "01F9ZQZJZJQZJZJZJZJZJZJZJZ",
  "customDay": 31,
  "customMonth": 12
}