Flash PX4IO Firmware
The latest PX4FMU firmware always includes the matching latest PX4IO firmware. The FMU will automatically try to update the PX4IO on boot. There is no need to flash the PX4IO manually anymore.
If you still have an older firmware on your PX4IO, auto-updating might fail after you flashed the latest PX4 firmware on your FMU. In this case, hold down the safety switch while powering up the system. PX4IO will then boot into bootloader mode which allows the FMU to properly update its firmware. You only need to do this once. Following upgrades of the PX4 firmware will successfully perform an auto-update again.