It's strange though:
Version 5.1.0(current)
Released: Apr 3, 2020
* Compatibility with Unity 2019.3.x
Original
Released: May 7, 2012
Last update is 3 of April, for compatibility with Unity 2019.3, which is the one I am using.
I believe the dev is still on it, but how can we communicate to him and tell him of the problems if his website is down?
I wouldn't ask for a refund if the product is working, but I see no way out... I also don't know how much time one has to ask for refund.