How can we improve WHMCS?

Hi, i would like to request for Delivery Order if possible.

Delivery order is similiar like invoice, just change the title from Invoice to Delivery Order, put the ref number based on our Invoice number and remove the price. What needed is item, quantity & description and invoice references number,

Example, during we created New Invoice, make addon option required "Delivery Order" or not, if we tick option required Delivery Order, so we can include Delivery Order and Invoice for customer soon.