curl --request POST \
  --url https://api.opencard.io/api/v1/application/accounts/{accountId}/billings \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "name_display": "Acme AB",
  "name_legal": "Acme AB",
  "organization_number": "5561234567",
  "country": "SE",
  "email_invoice": "finance@acme.se",
  "your_reference_invoice": "PO-12345",
  "product_transaction": true,
  "product_digital_receipt": false,
  "product_aland_index": false
}
'

const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    name_display: 'Acme AB',
    name_legal: 'Acme AB',
    organization_number: '5561234567',
    country: 'SE',
    email_invoice: 'finance@acme.se',
    your_reference_invoice: 'PO-12345',
    product_transaction: true,
    product_digital_receipt: false,
    product_aland_index: false
  })
};

fetch('https://api.opencard.io/api/v1/application/accounts/{accountId}/billings', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

import requests

url = "https://api.opencard.io/api/v1/application/accounts/{accountId}/billings"

payload = {
    "name_display": "Acme AB",
    "name_legal": "Acme AB",
    "organization_number": "5561234567",
    "country": "SE",
    "email_invoice": "finance@acme.se",
    "your_reference_invoice": "PO-12345",
    "product_transaction": True,
    "product_digital_receipt": False,
    "product_aland_index": False
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

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

print(response.text)

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://api.opencard.io/api/v1/application/accounts/{accountId}/billings",
  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([
    'name_display' => 'Acme AB',
    'name_legal' => 'Acme AB',
    'organization_number' => '5561234567',
    'country' => 'SE',
    'email_invoice' => 'finance@acme.se',
    'your_reference_invoice' => 'PO-12345',
    'product_transaction' => true,
    'product_digital_receipt' => false,
    'product_aland_index' => false
  ]),
  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;
}

{
  "id": 1,
  "name_display": "Acme AB",
  "product_transaction": true
}