I found where to show it in AwoCoupons Configuration -> Gift Certificate balance,
VM3.0.18 / Joomla 3.6.5
So i have changed to using Gift Certificates instead of Coupons so customer can use more than once.
For my first test of partial usage I created a customer and assigned 1000 points, which I then redeemed for a 10GBP gift certificate. I then used half of this paying for an order. Next I assigned them another 1000 points and redeemed them for another 10GBP gift certificate. The Balance now showed 14.60GBP. Next to the Balance was the text 'Apply' to apply this balance to the items in the cart. On applying the Balance to the order I see 'Gift Certificate' in the cart for the order amount (in this case 10.20GBP), and the order total reduced to zero.
Finally I click 'Confirm Purchase' ... however it comes back with 'Invalid data entered' and the Gift Certificate is removed. Also 'Apply' has gone.
If I logout and log back in the same happens.
Hope you can advise.