Pay-to-win
Also said as P2W, Pay for advantage
Players can buy an advantage over other players. Money beats skill, at least some of the time.
Refuse this in anything competitive. It breaks the thing the players came for, and those without money either leave or pay. Once they leave, the people who paid have nobody to beat. Even at small edges people will notice and complain, and the name will stick to you.
Say it
“No item sold for money can change damage, health, speed or matchmaking, in any mode. If a designer wants to sell one, they have to write down who loses to the person who bought it.”
Where you’ve seen it
Star Wars Battlefront II (2017) tied hero unlocks and upgrades to its loot and paid currency. The defence that this gave players "a sense of pride and accomplishment" became the most downvoted comment in Reddit's history, and EA turned the purchases off before launch.
Not to be confused with pay-to-skip
Paying to skip a grind saves time without beating anyone. It is milder, but be honest: you may have made that grind long in order to sell the skip.