function custnum_update_callback(rownum, prefix) {
var custnum = document.getElementById('custnum'+rownum).value;
- document.getElementById('enable_app'+rownum).disabled = (custnum == 0);
+ document.getElementById('enable_app'+rownum).disabled = (
+ custnum == 0 ||
+ num_open_invoices[rownum] < 2
+ );
% if ( $use_discounts ) {
select_discount_term(rownum, prefix);
% }