Ensure your game and the update .cia share the same region (e.g., both USA or both EUR) to avoid "refusal to update" errors.
The term in this context has no relation to the Central Intelligence Agency. It stands for "CTR Importable Archive," where CTR is the internal codename for the Nintendo 3DS hardware. A CIA file is a packaged format containing a 3DS game, update, or DLC, structured exactly as it would be installed to the console’s internal SD card or NAND memory. For legitimate users, CIAs are generated by Nintendo’s eShop servers during download. For users with custom firmware (CFW), CIAs can be created from cartridges or downloaded from online archives, allowing direct installation without the official eShop. pokemon ultra moon update 12 cia work