Splatoon 3 works again on recent versions of the game. If you got 2122-2403 when going online, this is your fix.
What was wrong
Our certificate patches are indexed by the game's build ID. When Nintendo ships a Splatoon 3 update the build ID changes, Atmosphère matches nothing — and applies nothing, silently. The game then rejects our certificate and you get 2122-2403 the moment you go online, with no clue as to why.
We were covering two build IDs. Anyone on 11.2.0 or the new 11.3.0 was getting nothing at all.
This build adds the missing one, for both s3certbypass and s3peername. Each patch ships under both filename forms — the short 40-character one and the 64-character padded one — because both conventions exist depending on your Atmosphère version, and a filename that doesn't match produces no message either.
Thanks to Kazu for the patches, and to cakita and the testers who reported it with their exact game version. That detail is what made it findable.
Honest limitation
The next Splatoon 3 update will break this again, the same silent way. Indexing by build ID means chasing every release.
The real fix is pattern-based patching rather than build-ID indexing, and we're working on it. In the meantime, kinnay publishes a script that scans instruction patterns in an NSO and generates the patch, which turns each new version into a few minutes of work rather than a day of it.
So: don't update Splatoon 3 if you can avoid it. If you already did, this build should have you covered.
Verified before shipping
All three build IDs carry the same instruction at the same offset (0x00157B20 ← MOV W10, #1), which confirms the targeted function does not move between versions.