const options = {
  method: 'POST',
  headers: {
    'x-spree-api-key': '<api-key>',
    Authorization: 'Bearer <token>',
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    filename: '<string>',
    content_type: '<string>',
    byte_size: 123,
    checksum: '<string>'
  })
};

fetch('http://{defaultHost}/api/v3/store/carts/{cart_id}/po_document', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

curl --request POST \
  --url http://{defaultHost}/api/v3/store/carts/{cart_id}/po_document \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'x-spree-api-key: <api-key>' \
  --data '
{
  "filename": "<string>",
  "content_type": "<string>",
  "byte_size": 123,
  "checksum": "<string>"
}
'

{
  "signed_id": "eyJfcmFpbHMiOnsiZGF0YSI6MSwiZXhwIjoiMjAyNi0wMS0xNlQxMjowMDowMC4wMDBaIiwicHVyIjoiYmxvYl9pZCJ9fQ==--a9cd29e72a70654182038480207bd929343f6a07",
  "filename": "purchase-order.pdf",
  "content_type": "application/pdf",
  "byte_size": 48210,
  "visibility": "private",
  "expires_at": "2026-01-16T12:00:00.000Z",
  "upload": {
    "method": "PUT",
    "url": "http://www.example.com/rails/active_storage/disk/eyJfcmFpbHMiOnsiZGF0YSI6eyJrZXkiOiIwc3NuNW5kM3RneWtwcWJndXdybGprZjNwbjc4IiwiY29udGVudF90eXBlIjoiYXBwbGljYXRpb24vcGRmIiwiY29udGVudF9sZW5ndGgiOjQ4MjEwLCJjaGVja3N1bSI6IjVXMjhrY2ZxcDlLMGY1djRZN2VyUkE9PSIsInNlcnZpY2VfbmFtZSI6InRlc3QifSwiZXhwIjoiMjAyNi0wMS0xNVQxMjowNTowMC4wMDBaIiwicHVyIjoiYmxvYl90b2tlbiJ9fQ==--d1ccdf3e94900f0c8f62feb07f43a3d33eb3b0df",
    "headers": {
      "Content-Type": "application/pdf"
    }
  }
}