Update 2.5 (13/09/2019):
Added a new define called "ZP43_SUPPORT" in the line 13 to support Zombie Plague versions since ZP 4.3 until the very first version (at least I think it does, but I didn't even test it and now nobody uses versions before ZP 4.3 though).
If your ZP version is 4.3 or older, then uncomment it and download (and install) cs_player_models_api
here (you will need the include to compile my plugin and its plugin "cs_player_models_api.amxx" installed in your server).
If your ZP version is 5.0 or newer, then leave as it is and it will work fine (you still need to have "#define "ZP_SUPPORT" uncommented to support any Zombie Plague Mod version).