If it says 4.0.0, the has succeeded.
The “400” in that string suggests the update needs at least firmware 4.0.0, which was old by the time v4.0.0 of the game released (late 2018). That mismatch hints the filename may have been copied from an earlier version or mislabeled. kirby star allies nspupdate 400verified work
A "working" update means no black screens, no "Unable to start software" error, and full Dream Friend compatibility. If it says 4