Recurring Invoices are invoices that are automatically created and sent to your customers on a regular schedule that you define (ex. Weekly, Monthly, Annually or Custom)
Recurring Invoicing is a premium feature billed at $0.50 per generated invoice, available to any paid or premium InvoiceASAP account. Recurring Invoices are not available to InvoiceASAP Free accounts.
Here are the support articles discussing Recurring Invoicing: