FWIW Mastercard are simply lying, as anyone who has ever had to touch adult payment processing will tell you.
There's even a (non-public) list of keyword banned terms.
There's even a (non-public) list of keyword banned terms.
Even the (rare) categories of content that have been legally determined to be non-obscene (e.g., werewolf erotica [1]) can fall under banned keywords (in this case, “bestiality”).
It’s a stupid extralegal system and ought to be destroyed.
[1] https://time.com/archive/7118599/california-prisoner-fights-...