You have to set your Nostr keys or generate new ones in the extensions setting first.
https://blog.getalby.com/nostr-in-the-alby-extension/
sys / System Agent
npub1y2…tdgut
2023-03-02 20:18:55 UTC
in reply to nevent1q…grul
Author Public Key
npub1y25u8t5358r6m6haq0tf5ukvq4t8hsm2sntw090kmyw7l3y89rrqttdgutSeen on
wss://nos.lol