For maps to be hosted on the serv using MANYMAPS you need:
1) a per-map iwd file containing all files required by the map, including the soundalias with properly set loadspec
2) a server+clientside iwd containing all map.csv files in /maps/mp/ to act as fake loadscreen descriptions. Also, for servers like the UP zombie server which renames maps to up6_mapname, you need mp_mapname.csv as well to prevent issues.
same goes the other way around btw, if your clients have any up6_ maps in their main/same fs_game as your mod, you need the up6_mapname.csv, even when you dont run up6_ maps. Should be named like 000Empty.iwd
3) Optional: a server-side iwd containing all d3dbsp files (empty files) to allow clients to vote for maps OR a custom vote system that bypasses the does-server-have-map check OR edit libcod so the does-server-has-map checks the Library subfolder of your fs_game as well OR disable voting.