A. If you get an a9lh error.
- First, make sure you really don't have a9lh. If you use b9sTool with a9lh, you will brick.
If you're sure this is a false positive: rename fastboot3DS/key.bin (this is your console unique NAND header) to danger_skip_a9lh.bin
Then rerun b9sTool and the error should be skipped and you get to the menu. Unlike other override files, this one will stay persistant and not be deleted.
B. You select "Install fastboot3DS", reset the system, but the system just boots up normal.
- Go to System Settings > Other Settings > Page 4 > System Update. Make sure to actually attempt to update with wifi on.
It should say "The system is up to date". Press ok and let the system fully reboot to home menu on its own.
Boot b9sTool again.
Choose "Install boot9strap", and hopefully you will see luma3ds config on next reboot.