To generate invoices automatically to your tenants you will have to toggle the "Turn on Automatic Invoice" Button. 

The Next step is to set when the invoices need to be created based on the next billing date.

In the below example, the invoices are set to generate 5 days before each lease's next billing date. 

When you are done click on "Submit" to save the changes. 

Example of Autoinvoice leases

In the below example the move-in date is 01/01/2021 and the next billing date is on "01/02/2021", according to the above settings invoice will be created 5 days before 01/02/2021. ie the invoice will be created on 27/01/2021.