Custom trim datapack/resource pack

Hi, 
I am struggling to update my resource pack to update my custom trim to the latest 1.21. The error that i'm getting in console is "Not all defined tags for registry ResourceKey[minecraft:root / minecraft:item] are present in data pack: frilcraft:trim_templates"
Not sure if that is the error that is causing it. But basically i'm unable to put the trim on the armour. I have changed the names of the files to take off the plural. I'm just a bit confused and i'm not finding much help about it.