Usually most PSP's do have some reserve rule, like keeping the 5% up to an X amount of sum, but with Adyen their team calculated the X amount to be in the millions - not one PSP (and we worked with all of them) had this.

So it was still percentage based? I’m a bit confused from your phrasing. Sounds like the problem was that 5% of X could end up being millions, because it had a high ceiling? That doesn’t sound so bad.