curl -X GET \
 /customers/{customerId}/billing-groups \
 --header "Authorization: Bearer <token>"

{
  "data": [
    {
      "name": "Billing of payments at the end of the month",
      "type": "end_of_month",
      "id": "01F9ZQZJZJQZJZJZJZJZJZJZJZ",
      "customDay": 31,
      "customMonth": 12
    }
  ],
  "meta": {
    "pagination": {
      "totalItems": 123,
      "itemsPerPage": 123,
      "currentPage": 123,
      "lastPage": 123,
      "pageTotalItems": 123
    }
  }
}