> Bigger purchases give more, because the percentage lost to fees are lower.
Encouraging bulk purchases seems like an orthogonal problem to allowing users to choose the amount. You could always allow users to choose the amount and just include the transaction fee.
> after the purchase is made, it's not real money, and if it were, I'd be a financial institution and break the rules of all major card networks
If card networks are operating in the country, they'd have to abide by the country's rules too.
But also, I don't think that's how it works. It says "Developers must be obligated to provide an equivalence in real currency clearly and transparently next to the premium virtual currency before each transaction." (translated to English, but) - IIUC this means that if you sell a skin for "10 coins" you have to show the cost in real world money at the same time, e.g. maybe $1.9 one day, maybe $2.2 another day, based on the cost to purchase said coins. Or you could change the skin price from 10 to 11 or whatever if you want to keep the real money cost the same. It's not forcing any financial changes on you, just making you display a number.