I mean the relay collects digital stamps into its own wallet. When the Keychat wallet has a balance, Keychat will request 32 ecash tokens of 1 sat each from the Cashu mint. These are what we call digital stamps. A digital stamp is simply a piece of data, since ecash tokens are bearer tokens. When a user sends a message, the digital stamp is automatically appended to message. When the relay receives the message, it redeems the digital stamp. At the moment, we’re the only ones advocating for and using digital stamps.