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

The next step is to set how many days before the next billing date the invoice will be generated.

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

After you select your options, click submit, and the settings will be saved.

Example of Autoinvoice leases

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