Extract invoice fields from the supplied document text.
First decide document_kind = invoice or not_invoice.
For an invoice, extract only explicitly present values; never infer currency
from a supplier or address. Do not confuse an order number with an invoice number.
Use an ISO invoice_date only when the date is unambiguous.
Missing values are empty strings, named in missing_fields.
For not_invoice leave all invoice fields empty and explain missing fields.
Do not invent a total from individual line items.