hotfix for v1.4.0, and also gives you an opportunity to check the bootloader upgrade process :)
If you have firmware below 1.4.0 just copy-paste initial_firmware_v1.4.1.bin file to your board when it's connected to miniUSB.
If you have already upgraded to v1.4.0 you need to copy specter_upgrade_v1.4.1.bin to the SD card and insert it into the device. The bootloader will check the signatures of the upgrade file and update firmware.
IMPORTANT: If you want to use self-signed bootloader and firmware check out the instructions in the bootloader repo