Coupon Problem – Negative Amount

I tried to generate a coupon and using an amount for example 150 €, when I use it on an experience of a lower amount, the system calculates a negative account to be paid.

See screenshot (view)

example coupon from € 150 purchase experience from € 70 I have a balance of € 80 that I will not be able to use and therefore an amount due of € 0.
or better, if possible, to deduct the 70 € of the experience from the coupon and be able to take advantage of the rest at another time?
I hope I have explained myself correctly.

Thanks.