My texture is not loading

I have followed this video: https://www.youtube.com/watch?v=aaJ8XgMAOno,
and the texture does not seem to be rendered on the model.
The model appears to be mostly black.
Here is the file structure:
    ->assets:
        ->minecraft:
            ->models:
                ->item:
                   ->carrot_on_a_stick.json
                   ->system_upgrade.json
            ->textures:
                ->custom:
                    ->back_systemupgrade.png
                    ->front_gray.png

and here is what is going on inside carrot_on_a_stick.json
{
    "parent": "item/handheld",
    "textures": {
     "layer0": "item/carrot_on_a_stick"
    },
   
    "overrides": [
     { "predicate": {"custom_model_data": 1324001}, "model": "item/system_upgrade"}
   
    ]

}

I have no Idea why it is not rendering the texture.