If a client normally receives a monthly facial as part of their membership but isn't able to come in for 2 months, they should be able to take those 2 unused facials and upgrade to a higher level facial. For example, the membership provides a monthly Signature Facial. But, the client hasn't been to the office in 2 months. The value of the services owed equates to that of a higher valued facial (Hydrafacial for example). They should be able to "swap" the 2 unused facials and the system should be able to "pick them up" from the client's unused vouchers and apply them to the Hydrafacial, instead.