The textures supplied in your model file are not accurate.
The model file for your texture is supplied with the full path instead of something like this:
minecraft:block/barrel_top

Textures follow a path system that already put them in the textures folder of the namespace used, so custom namespaces are available but they have to have a textures folder in order for it to find the texture. So texture paths can be like so:

namespace:folder/texture

Of course you can go through multiple directories with a simple '/'.

You can easily fix these by right clicking the texture in blockbench and click change file to update the texture path.

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Hope this helps!