You can set how many Invoices will be created by setting up the Maximum # of Invoice Created. If you want an unlimited number of Invoice creations you can input 0 as the maximum number of Invoices created. 

You can also choose how you want to limit your On-Demand Invoice, it could be every time an invoice is paid or every time an invoice is created. If your On-Demand link reaches the limit, you are no longer able to create a new Invoice.