1. Is there any coupon plugin that can be used to manage offline vouchers?
I issue real coupon card like the one for mobile phone balance topup. The code on the coupon can be used to pay for products on my webstore.
If not used up then the customer can come back later and buy other products with it. Until the balance is zero and the store should then refuse the code.
2. Is there plugin (much better if also having the above feature in one plugin) that can use unit price/credit instead of currency price.
i.e: The coupon is sold for $5 and having 6 credits/units in it (like minute or number of sms for mobile phone). And this units/credit is used to pay for products (which priced with unit/credit also)