Edit Json file

[mcmxl22]

I am trying to add key\value pairs to a Json file. I can write one pair to the file but I can't figure out how to append additional pairs. When I try, it just replaces the current pair. I have tried following this tutorial but I get key errors.

import json 

product_data =  "{}"

product = input("Enter product name. ")
price = input("enter product price. ")
new_product = {product:price} 

load = json.loads(product_data)

load.update(new_product) 

with open("Product.json", "r+") as file:
    json.dump(load, file)

console output:

Output:
Enter product name. milk
enter product price. 2.99

File output:

Output:
{"milk": "2.99"}