Swappable is a User Interface for accessing the blockchain, so transactions do not happen on Swappable, but do so on the blockchain.
Transactions are signed via the interaction of the platform with your selected cryptocurrency wallet, ensuring maximum security provided by blockchain technology.
Swappable never takes custody of your NFTs or your private keys. Plus, deals via Swappable are executed atomically. So either the whole deal happens, or none of it does.