What is the Whiteout Survival V4 private server?
It's a separate copy of Whiteout Survival run by a player community, not by Century Games. Progress is much faster than in the official game: you start at VIP 8 with 180,000 Diamonds, Gen 1–8 heroes are available from launch, and a fresh State opens every 48 hours, so there's always a new server to climb.
Shop packs are bought with Frost Stars, which you earn from daily missions, the Arena and events. That's why free players can keep up.