I have the same issue with this post, and I've checked your demo site front end & back end, have the same issue as well (http://demo.awocoupon.com/aworewards/invitation-form, I logged in with "manger" account).
The shorten registration url does not work and always appear long url even after click regenerate link button.
Do you know how to fix it?
p.s. All API / configuration settings mentioned in your discussion was checked.