The author of piosolver stop providing the free version for obvious reasons.
The reasons are not obvious to me. Why did they stop? Cheating? Annoying support requests? Could sell for more money?
My idea is the free version has some drawbacks:
(1) people don't want to pay will stick with this free version
(2) it's like a sample pack for solver, you may download the free version and say "it's not so good after all". Bad for business
(3) it increase the probability of been hacked