[joligario]

Use quest globals.

sub EVENT_ITEM {
  my $cash = $platinum * 1000 + $gold * 100 + $silver * 10 + $copper;

  if ($cash > 0) {
    if (defined($qglobals{credit})) {
      quest::setglobal("credit",$qglobals{credit}+$cash,0,"F");
    }
    else {
      quest::setglobal("credit",$cash,0,"F");
    }
  }
  else {
    plugin::return_items(\%itemcount);
  }
}

Didn't test or check this for errors, but it is something you can start with.