Thus, after the client took the services during the time that was reserved by them.
Click on the same appointment on the calendar.
2. Click on the "Completed" to change the status once client took the service.
After you select "completed," the system will take you to the "Invoice" module, where staff members or admin may generate an invoice under the client's name and choose a payment option.
Additionally, for your reference, below is the video tutorial.