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 ["EVENT", , "cashu string"]. When the relay receives the message, it redeems the digital stamp.