I was speaking to Anum from your support team, I was told to add my suggestion here.
For our business, we have subcontractors working for us and for work to be proceeded we would send them a purchase order to carry out the work and once the work has been completed they would send us an invoice for the work they have carried out. At the moment there's nothing like this as I've been told.
A purchase order is different for our business to what it is on kashflow... I understand it is an accounting software so this is not an important topic however it's never a bad idea to increase the range of services you provide to match different businesses.
Maybe add a subcontractors option.