In Kashflow already there is project field available for user to input values while creating a Purchase order or Invoice, which allows users to categorising each line item in Purchase Order or in Invoice as per project. But the Project field does not get displayed in Purchase Order or in Invoice once it is saved.
Displaying the project values in Purchase order or in Invoice will help user to show there customers/vendors in more detailed each line categorization with Purchase order/Invoice.
To add a project field in Invoice and Purchase Invoices go to 'Project Settings' (link here https://app.kashflow.com/ProjectOptions.asp) and select the option to include the project name on invoices and separately purchase invoices. Quotes and PO have a project field in the header level