Why would you use 12V when it requires 24V.?

If you are powering a 12V relay then you still need 24V for the AXBB-E outputs to work but use the 12V supply for the relay by connecting both 12v and 24V Zero volts together then connecting the 12V + to the relay coil V+ terminal, then run a wire from AXBB-E output you are using to the Relay 0v terminal.