
my requirement is to discard those sales quotation lines which have checkbox enabled in the sales quotation line and stop that particular line to convert to sales order when we confirm the sales quotation..
For that you should use this event subscriber:
[EventSubscriber(ObjectType::Codeunit, Codeunit::"Sales-Quote to Order", 'OnBeforeInsertSalesOrderLine', '', false, false)]
local procedure OnBeforeInsertSalesOrderLine(var SalesOrderLine: Record "Sales Line"; SalesOrderHeader: Record "Sales Header"; SalesQuoteLine: Record "Sales Line"; SalesQuoteHeader: Record "Sales Header");
begin
end;