At its core, ZaZ Animation Pack (ZAP) is a . While a typical animation mod might just change how your character swings a sword, ZAP provides the underlying "logic" for complex interactions.
You must use an animation engine like Fores New Idles in Skyrim (FNIS) or the newer Pandora Behavior Engine to register the new animations.
Later versions were taken over by different authors and introduced changes that some users found controversial or buggy compared to the 8+ baseline. Essential Requirements
If you are using mods like SexLab, you often have to go into the MCM and click "Install Animations" or "Register" to make them see the ZAP library.
This almost always means you forgot to run FNIS/Pandora after installing the mod.