Hi, yesterday, I needed to have some of my BTC swapped for ETH. So I wondered what would be the fastest way to do that and I found changenow.io - a coin swap platform. Basically, without needing to create an account or anything, I just send my BTC to a wallet provided by this platform and it sends me back ETH to the wallet address provided by me.

So I was wondering how does that work. Do they use a centralized exchange like Binance or Coinbase and somehow swap on them in which case they're somewhat of a middleman or do they use some other methods that I'm not aware of?

Thanks.