Pass preselected custom dates in the preSelectedTerms input, or the
pre-selected-terms HTML attribute, as payment_term_dates values in
yyyy-MM-dd ISO calendar-date format.
Custom dates are displayed in MM/DD/YYYY format. The
outputPaymentTermForm event emits valid custom dates in each term's
payment_dates array as yyyy-MM-dd, preserving the selected calendar day without a
timezone conversion. A valid date entered as M/D/YYYY is normalized to the same ISO calendar date.
Empty dates are emitted as null and keep the form invalid. Other invalid date text is returned unchanged
with valid set to false.