If i close my account and I have a 20$ coupon, and in my "Uninvoiced Balance" 10$ do I have to pay or the coupon is sufficient

Balances will be applied to unused account credits before they will result in payment card charges.

So, if you close your account and have a $20 credit and a balance of $10 when closing, the balance will be applied to your credit and won't generate any charges.