Retainer instalment not taxed

Hello!  I am struggling to understand something in the invoices.  In my state in order for a retainer to not be taxed it has to be labeled as non-refundable retainer on the invoice.  I see there isn’t a place to add a note on the retainer installment but I can add a note on the invoice itself.  So my question is if I add the installment of a retainer at 50% not taxed and the client decides to pay the full amount upfront anyway will it know to not tax the 50% retainer, or will it tax the whole thing?  Thanks!