Loot table doesnt workk

I have a problem with a loot table and i dont know how to add nbt data about a custom enchantment im making, Please help 
{
    "pools": [
        {
            "rolls": 1,
            "entries": [
                {
                    "type": "item",
                    "weight": 1,
                    "name": "minecraft:enchanted_book",
                    "functions": [
                        {
                            "function": "set_nbt",
                            "nbt": "[stored_enchantments={levels:{"enchant:customenchantment":1}}]"
                        },
                        {
                            "function": "set_count",
                            "count": 1
                        }
                    ]
                }