If you wish to set up a new one-time payment after the lease has already been created, open the ‘Invoices’ tab for the relevant lease. (See here if you need more info to locate your ‘Invoices’ tab.)
Once the Invoices tab is open, simply click the ‘Add Invoice Item’ at the top of that page. This will add an additional row for the new invoice, in which you can define the payment type, due date, and amount. Once finalized, your tenant will automatically receive the invoice in the Tenant Portal.