The Progress Payment function is located on the Summary Tab’s Details section.
The Payment Schedule will be pre filled with an Initial Payment and Final Balance amounts based on the Default Deposit Percent you added on the Settings page under the Settings section. The Initial Payment date will be the the current date and the Final Balance date will be set for 14 days of the current date. These dates are both able to be edited by clicking on the date field and bringing up the date picker.
You can add more rows to the Payment Schedule by choosing the + icon. Fill out the payment description such as Second Payment, then you can specify either an amount or a percentage in either field and all other payments will be automatically calculated for you.

The payment schedule will then be available on the Invoice sub tab ready to send an invoice to Xero or QuickBooks and send to the client for payment.