Diablo Immortal, like many mobile games, can be extremely expensive for high-level players, so you can't really blame anyone for seeking a discount. Unfortunately, players that purchased Eternal Orbs from third-party websites have had their in-game purchases revoked, leaving them with massive debts that many can't pay off.
Eternal Orbs are Diablo Immortal's premium currency. You can purchase Orbs directly from the in-game store for anywhere from $0.99 USD for 60 to $99.99 for 7,200. Orbs can be exchanged for cosmetics (which will run you between 1,000 to 1,650, depending on the cosmetic), Reforge Stones to re-roll your equipment, or Legendary Crests for a chance at getting Legendary Gems from Elder Rifts. That last one will cost you 160 Orbs and is the main way players improve their character's power.
Purchasing all those Orbs can get extremely expensive, so many turned to third-party sellers where those 7,200 packages for a discount--sometimes as little as $10 USD. Unfortunately, it turns out that these third-party websites were likely breaking Blizzard's terms of service, either by offering these discounts thanks to stolen credit cards, gift cards, or by taking advantage of regional price differences.
When Blizzard banned all these third-party purchases, it deducted these ill-gotten Orbs from player accounts, leaving them with negative balances. Players with negative balances can't join parties or participate in group activities such as Elder Rifts or dungeons. But buying their way out of debt legitimately can cost hundreds or even thousands of dollars.
As noted by PCGamesN, Reddit threads have popped up warning players of what's happened with third-party Eternal Orb purchases. One such player, a high-level Wizard named Shia, received a -2,491,025 Orb debt that would have cost over $35,000 to repay. In an interview with jtisallbusiness (the same guy who discovered they can't play PvP after spending $100,000 because the matchmaker couldn't find an equal-level opponent), Shia said that they're probably just going to quit rather than pay off the debt.