ClubWPT Gold isn't a real-money poker site in the regulated-market sense — it runs on the sweepstakes model, the same legal structure used by social casino apps, which is why it's available almost nationwide instead of being locked to a handful of regulated states.
Play uses two currencies: Gold Coins, which have no cash value and exist purely for practice/entertainment, and Sweeps Coins, which are awarded alongside Gold Coin purchases and can be redeemed for cash at a 1:1 rate (minimum 20 SC / $20, up to $2,500 per day).
It's branded around the World Poker Tour, and because it runs under sweepstakes law rather than state gaming licenses, it's legal in most of the country — but a handful of states block it entirely, and California runs under a special limited redemption schedule.