First of all, thanks for all support, been testing a lot before launching the system but encountered several bugs.
1 - Coupons are not deleted once used and are available to use again.
I noticed that coupons are not deleted from payment history so I used one, completed the order, then use it again and it worked again.
In VM I have the option "delete coupons" on the status accepted which is the one the order turns to.
2 - Points can be changed to coupons even when this are below the minimum to generate value.
This one is a sneaky one.
A customer has 8.21 points - so we change points to coupons and it changes 8 (1 €) with our settings.
The 0.21 left can be changed to coupons without limit and the value stays the same as 0.21 €.
Each time you click you get an email with a new coupon code and it says the value is of 2 €
In the Payment History you will see each of this coupons however with value 0.
I though solution could be to set minimum payout amount to 2 but strangely a customer with 5.47 points could not change them to coupons (button didnt appear).