Hello, obviously we don't know what you're doing wrong, because if you don't post some logs or other details there is no chance to help with anything. Maybe your emmc is faulty and it will just never work...
Once run, multitool will drop a file on the FAT partition called dmesg.multitool.log with the kernel dmesg log you can post here for inspection.
However I would rather erase the internal emmc and try armbian from sdcard instead of burning on emmc.
