This is a classic region mismatch. Your base Ultra Moon game and the 1.2 update CIA have different Title IDs. Verify whether your base game is the US, European, or World Edition, and source the exact corresponding update file.
As players progressed through the storyline, they discovered that The Archaeologist was not what they seemed. A shocking twist revealed that this mysterious figure was, in fact, a long-lost professor from a distant land, thought to be extinct.
It sounds like you’re referring to a for Pokémon Ultra Moon on the 3DS, specifically a “World” (region-free) CIA file for use with custom firmware (like Luma3DS on a hacked console). pokemon ultra moon update 12 3ds world cia exclusive
Find the Pokemon_Ultra_Moon_v1.2_USA_3DS-BigBlueMenu.cia (or EUR equivalent) from a reputable homebrew source.
Pokémon Ultra Moon Update 1.2: 3DS World CIA Exclusive Guide This is a classic region mismatch
Keeping your Pokémon Ultra Moon updated to 1.2 ensures you have the most stable, albeit final, experience of the Alola region on the 3DS.
A file is a format used on the Nintendo 3DS to install digital content, including full games, downloadable content (DLC), and software updates. As players progressed through the storyline, they discovered
You are trying to install a European update on a North American game copy, or vice versa.