Thanks for reaching out to us Atricio.
The Service Coupon Balance represents the difference between what you have paid for a subscription, and what has actually been deducted from that payment for your current usage. So right now you have paid annually for your subscription, but the system has only deducted the amount for the initial month. Then, the system will deduct remaining months from your Service Coupon Balance until your annual renewal is due again.
Please let us know if you have any other questions or confusion.