Hello @PJ11
Welcome to QuickFile 
There are a few options to entering data into QuickFile, but I believe the best approach for a business such as yours would be either to import sales on a regular basis (e.g. weekly) and re-create the invoices within your QuickFile account, or bulk-enter sales.
Bulk entering sales would likely to be the most efficient approach as it would require you just creating one invoice to represent sales within a period. So you could create a new invoice each week for example (or even day if you sales volume is high). This invoice would be assigned to a generic client such as “Amazon Sales” or “Daily Takings”.
Both of them have their pros and cons - it depends on how much data you want in your QuickFile account and your own processes.
These guides may also help: