The previous answer isn't very helpful.

VS do of course fly direct from Manchester to Las Vegas. Perhaps not daily but a couple of times per week. You can book one-ways ex-MAN and returns, but I see the same issue for LAS-MAN.

I can only imagine that there is an IT glitch (since you can buy cash tickets the route must be legal), so you should call Flying Club.

(as always, surcharges ex-USA are higher - even worse post Brexit / sterling devaluation - so keep that in mind)