If you remain stuck, do not turn to shady YouTube tutorials. Visit the official or the /r/3dshacks subreddit. Provide them with your console version, your SD card size, and the exact error text. They have seen this error a thousand times and will get you back on track.
If you are reading this, you have likely hit a frustrating red wall while trying to hack (or "mod") your Nintendo 3DS. You’ve followed a guide step-by-step, placed the necessary files on your SD card, booted into the Homebrew Launcher, launched SafeB9SInstaller ... and instead of a beautiful blue installation screen, you are staring at an error message: failed to open safeb9sinstaller.bin
Take a deep breath, safely eject your SD card, and walk through Method 1 to Method 5. By the time you finish, you will likely be staring at the SafeB9SInstaller’s beautiful "Boot9strap installed successfully" message. If you remain stuck, do not turn to shady YouTube tutorials