Keychat has introduced the sats stamp concept, which is quite similar to what you’re talking about.👇
Keychat is a chat app, built on Bitcoin ecash, Nostr protocol and Signal/MLS protocol.
Keychat is inspired by the postal system — stamps, post offices, letters.
Keychat uses Bitcoin ecash as stamps and Nostr relays as post offices.
Keychat uses Signal/MLS protocol to ensure message encryption security and meta-data privacy.