Crafting recipe not working

Hello, i'm trying to make a crafting recipe, but no matter what I do, I get errors saying that minecraft couldn't parse my recipe file. Here's the content:
{
    "type": "minecraft:crafting_shaped",
    "pattern": [
        "LLL",
        "WCW",
        "LIL"
    ],
    "key": {
        "L": {
            "item": "minecraft:leather"
        },
        "W": {
            "tag": "minecraft:wool"
        },
        "C": {
            "tag": "minecraft:chests/wooden"
        },
        "I": {
            "item": "minecraft:iron_ingot"
        }
    },
    "result": {
        "id": "backpackmod:backpack",
        "count": 1
    }
}