Getting required fields for registrars to order a domain via the API(AddOrder, Parameter - domain fields)

[Leonid]

Good day,

How can I find out which additional fields are required by the registrar? I am sending the data using the following structure:

$order['domainfields']['0'] = base64_encode(serialize([
    12 => "2022-02-02",
    13 => "2022-02-03",
    14 => "2022-02-04",
    15 => "2022-02-05",
    16 => "No",
    17 => "2022-02-06",
    18 => "2022-02-07",
]));

However, I do not know where to obtain the ID for each specific field.