An advance invoice reports a prepayment: a NORMAL invoice whose lines are
advance charges (advanceData.advanceIndicator). Any line not already marked
is marked as an advance. Later, the final invoice (végszámla) settles it —
build that with buildInvoice, adding a deduction line per advance whose
advance option references this invoice's number and whose amounts are
negative.
Build an advance invoice (előlegszámla).
An advance invoice reports a prepayment: a NORMAL invoice whose lines are advance charges (
advanceData.advanceIndicator). Any line not already marked is marked as an advance. Later, the final invoice (végszámla) settles it — build that withbuildInvoice, adding a deduction line per advance whoseadvanceoption references this invoice's number and whose amounts are negative.