This feature allows you to create a payment link which can then be sent to your client via a customised email. Your client can then pay your fee, invoice or deposit using your default payment options.
You set up a payment Request from My Sales -> Payment Request
Just input the payment request description(what the payment is for), the amount owed and any admin notes (which are kept hidden from the customer). Once this information has been submitted a payment link is generated which links to your default payment option (for example your PayPal account). On submission a customised email will open, in your email account. Just enter the customer's email address and hit "send".
The customer can then click on the link and checkout. Once the payment has been made you will receive notification by email and the payment will also be recorded in your sales history.