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we just try to be prepared in an unforeseen event where all Predeyx user wants to withdraw at the same time
That's very important. Some of the other services I wrote about have tarnished reputations because users have had difficulty recovering their funds. Trust is very important here, since you're asking bitcoiners to risk their sats on a zero-sum game.
That said, remember that if everyone tries to sell at once, the prices will move dramatically. For whatever reason, we tend towards loading up on the Yes side, so if we all try to sell the price will drop and you'll end up paying out much less than current price x shares.
We should be doing the same thing what Block/CashApp is doing i.e making 10% APY. I think to make it fair we should NOT charge 1 sat flat fee for inbound payments (User wallet -> Predyx/Market wallet) But we should charge 1 sat flat fees for all outbound payments (Predyx User Wallet and Market Wallet -> User's external wallet)
Exactly. Bitcoin is a capital asset, so you want to hold it on your end and do useful stuff with it that doesn't reduce your ability to cover payments. Whatever yield you manage can offset user fees, which reduces trading frictions and improves your competitive advantage over other betting sites. Deepening your markets in that way will then increase the value of the information product that you're creating.