I take this file and import into Zoho Reports.

I want to be able to handle post-paid invoices (so import everything as before including all the invoice paid dates and then start marking the invoice paid dates in Zoho Reports)

My problem is that Payment Dates are managed in a separate spreadsheet - therefore, I have spent a few hours correlating payments to invoices and have a base to start with... Moving forwards, I want to import the orders (without the payment details because it takes 1-2 hours each time) 

I want to import payment dates and then simply import the orders file daily and have it remember the dates... 

I'm using the Delete and add import because I have a full file each time and it saves me filtering through the data and flagging items that have already been imported...