The bios file
cdimono1.zip can be obtained from a modern MAME romset.
It should be put in this folder
The file should contain
zx405042p__cdi_slave_2.0__b43t__zzmk9213.mc68hc705c8a_withtestrom.7206, if not you got an old (unsupported) version of
There are also two optional files,
cdimono2.zip (the file extension may also be .7z).
The CD-i uses chd images compatible with MAME 0.239.
The same_cdi core does currently not support DVC (Digital Video Cartridge) games.