The NSP file may be incomplete or corrupted during extraction, especially if using 7-Zip on multi-part archives (WinRAR is often recommended as an alternative).
(usually the largest file). If you try to open an update file (NSP) directly, it will throw this error. Install to NAND the nsp file is missing a programtype nca upd
If you are trying to create a merged Base + Update NSP and encountering this error, use a reliable method: The NSP file may be incomplete or corrupted