Couple days of work and I created simple node-red wiring and modified HostSpot portal page to send guest vouchers by SMS.
I have used node-red because now I can send vouchers however I want, and it is very easy to implement. Node-red is using UniFi API to talk with Controller and create vouchers on demand.
Ps. I am curious when UBNT will correct AngularJS tempate to display flag icons like below