author_id is for discord UserIDs, and the no token is most likely because you didn't create an account. Account creation is free but limited use, 50 results cap and won't show information dating more than 1 month old.
I built illumi.icu. Paste any Discord User ID from 160+ servers I've scraped and see all their messages, which servers they were in, timestamps. Next: AI that auto-detects leaked emails/phone numbers/socials from message history. Free tier with limitations available.