Can't add Heads Plugin API 2 [1.13 - 1.16] to my server

Hey,

I tried to install HeadsInventory on my 1.15.2 server, but to install it i need another plugin called Heads Plugin API 2 (https://aternos.org/addons/a/spigot/19672). I tried it several times to add this second plugin to my server but it doesn't work and it's not in the plugin files.

Can somebody help me?