You must ensure the DLC region matches your base game. If you have the North American version of Stretchmo, you need the USA DLC CIA; otherwise, the game won't recognize the extra levels.
Subreddits like r/3dspiracy have extensive megathreads and guides on how to safely find and install DLC for games that are no longer available for purchase. Safety and Requirements Stretchmo 3DS (USA) DLC CIA
Stretchmo (known as Fullblox in Europe) is the fourth game in the popular Pushmo puzzle series developed by Intelligent Systems. Unlike its predecessors, Stretchmo was released as a free download on the Nintendo eShop, giving players a set of introductory puzzles for free. To play the full game, users had to purchase "Attractions" (DLC packs) through an in-game menu. The DLC "CIA" Situation You must ensure the DLC region matches your base game
Since sharing direct download links to copyrighted CIA files is often restricted on major platforms, the 3DS community relies on a few well-known archives: Safety and Requirements Stretchmo (known as Fullblox in
To use these files, your 3DS must be running custom firmware like Luma3DS. You typically install them using a tool called FBI . Where to Look (Community Resources)