The Moi.idl file is no longer used, as of MoI4:
https://moi3d.com/forum/index.php?webtag=MOI&msg=10518.5

The old, (but latest?) (2015) Moi.idl file is here:
https://moi3d.com/forum/index.php?webtag=MOI&msg=7262.2

- Brian