Square Appointments: Can my customers use a discount code when booking?

[DanielleK]

I send invoices to my clients and they pay online. Is there a way to set up a discount code that they will be able to enter at the time of payment? 
For example, right now I have a 10% discount set up that I add to certain invoices before sending. 
But what I'm looking to be able to do is give certain clients a discount code, so that they would place their order, I would send them their invoice, and then they are able to input that discount code when paying the invoice to pay the adjsuted amount. 
Is this possible?