How do payment processors like bitpay work? How do payment processors like bitpay work?
As far as i understood you can only have one address per key pair, so do they generate a whole new pair for every payment? Or can this be done using HDWallets?
They generate a private key and an address corresponding to that private key everytime you see BitPay's payment page (even if you don't pay they keep the private key and that private key is generated only for one payment). When they receive payment to that address, they send your money from that address to their main wallet.