I know this is almost 3 years later, but I just ran into the same issue.
you were 2 characters off getting this to work

Code: Select all
/ip dhcp-server option
add code=43 name=APC value=0x010431415043
From APC's web site: Option 43 = 0x01 0x04 0x31 0x41 0x50 0x43