Cemu found a key for your title ID, but the key is incorrect—either corrupted, from a different region, or for a different game version (e.g., update vs. base game).
The file is typically named exactly "keys.txt" (or "Cemu Keys.txt" in a descriptive context) and placed in Cemu’s keys directory so the emulator can automatically read them.
Save it as keys.txt in your Cemu root. That’s it. No fancy formatting needed.
file must be placed in the root directory of the Cemu folder. The format inside the file is strict, typically following a pattern such as: [32-character Hex Title Key] # [Game Name]