In myBooks you can create a duplicate copy of the existing invoice instead of creating a new one with the same customer details.
Goto Transactions > Invoices > Invoice list page opens
Place the cursor on the particular invoice that you wish to create a duplicate invoice. In the right-side corner, next to the download symbol you can find the duplicate symbol, just click on it.
Duplicate invoice gets created for the same customer with the same amount of previously created invoice.