Recrurring Invoices - Month Before

Hello,
I am setting up a recurring invoice and want it to show a month behind in the item box. For example, it will go out on June 1 but I want the item to be May. Is there a variable for this?

Also, if anyone has a list of the variables that would be great because I can’t find them anywhere.

Thank you!

You can use :MONTH-1

Click the question mark to the right of the frequency select to see all the values.

Thank you!