If this is dealt with via support ticket, will the results still be posted here? I think several people have reported this issue. It would be useful if it were fixed.
The problem seems to be that the record id cannot be entered using the interface so of course nothing is sent to the cart page. I expect your problem has been resolved now Alistair but in case it hasn't yet, I think the problem is the missing ID field between the "" below:
$row_romeroRecordset1 = WAEC_findRecordMySQL($romeroRecordset1, "", $ATC_itemID);
eg $romeroRecordset1, "item_id", $ATC_itemID