Payment Template - Amount Outstanding

Hi There,

A client recently paid a part payment for an invoice we sent them.

When the invoice went over the required time for payment the customer rang me to say why they had been sent a reminder. To which I replied you made a part payment.
Their response was "oh, we didn't spot that, can you make it more obvious next time?"

Can we add "Amount Outstanding" on the Payment Template and if so how would one do it?

Many thanks.

Conrad