If Windows or macOS claims your SD card has plenty of space, but the 3DS still triggers a full partition error, you likely have ghost data or unindexed blocks:
Use tools like Remote Install in FBI or the "Boop" utility on your PC. This streams the data directly to the 3DS over Wi-Fi, meaning you only need enough space for the final installed game, not the installer file itself. 3. Format Your SD Card 0xc86044d2 full