While AppointmentGuru doesn't directly support recording a client payment credit (payments need to be logged against an existing appointment), it is possible to create appointments into the future and log payments against these appointments.

For example, let's say an appointment costs R100 and your client has paid you R400. The solution is to create 4 appointments on that client's account (you can create them into the future). You can then track the payment against these appointments and they will go green (status = paid).

You can move these appointments around after the fact using the reschedule functionality.