zombie ignore datapack

Hey everyone,
I'm trying to make a simple datapack in Minecraft (Java 1.21.1) where zombies ignore players who have a specific tag (zombie_immune). The idea is that if a player has that tag, zombies won't target or attack them.
I created the proper folder structure, added pack.mcmeta, made the tick.mcfunction and clear_target.mcfunction files, and set everything up. I zipped the datapack and placed it in the world’s datapacks folder.
But when I do /function, none of my custom functions show up (like zombie:tick). And in general, the datapack doesn’t seem to be doing anything.
 I already tried:
Using /reload after installing

Making sure pack.mcmeta is at the root of the .zip

Confirmed file paths and syntax

Still no luck. Any idea what might be going wrong? Thanks in advance!