Piefed is an entirely different software (“mbin”, a continuation of “kbin”) - speaks ActivityPub but is not a Lemmy API. Reading other comments in other posts, there’s one (and only one) app being mentioned as having beta support for Mbin (code, API) servers.

Edit: 2025-06-12 1300 UTC, the https://piefed.social/ is broken and returning error 500 (as in, it’s 100% broken for users)