The ability to link invoices to appointments would be immensely beneficial! There should be a menu option to "schedule an appointment" when you select an invoice. When you create an appointment from an invoice the data (services and costs) from that invoice would be automatically copied to an appointment (which you could further edit) eliminating the need to manually reenter everything or trying to link them on the spot upon checkout!
This feature in conjunction with the ability to set unit measurements in services would streamline Square for most trades professionals.
