One-time payments can be added when you first create a lease or afterward. If you are creating a new lease, you can add one-time payments in the ‘Deposits and Fees’ tab from the lease creation menu. There, you can add a security deposit, last month’s rent prepayment, as well as any other one-time fees (e.g., move-in fees).
If you’d like to add additional one-time payments after a lease has been created, you can do some from the Invoices Schedule. For details on adding one-time charges once the lease is set up, see here.