Shopify cartDiscountCodesUpdate storefront API cartid

I want to apply discount coupon code to the cart page, I am trying to use the storefront API cartDiscountCodesUpdate which expect the cart id. How can I get this cart id. Here is what I tried. I have created the webhook cart/create which has payload id in the form of string something like '1eef2aa2c2b2e889ec325db72f0877ec'.

Then I tried calling this id which I got from cart/create response in storefront API cartDiscountCodesUpdate like:

 mutation cartDiscountCodesUpdate($cartId: ID!, $discountCodes: [String!]) {
  cartDiscountCodesUpdate(cartId: $cartId, discountCodes: $discountCodes) {
   cart {
     id
   }
   userErrors {
     field
     message
   }
  }
 }

Query Varialbe: { "cartId": "gid://shopify/Cart/1eef2aa2c2b2e889ec325db72f0877ec", "discountCodes": [ "64J1ZQMBN9W5" ] }

But its response with below error. I think its the issue with incorrect cart id. Can anyone help me how to get cart id after the cart is created?

Response from cartDiscountCodesUpdate storefront API.

 {
  "data": {
  "cartDiscountCodesUpdate": {
  "cart": null,
  "userErrors": [
    {
      "field": [
        "cartId"
      ],
      "message": "The specified cart does not exist."
    }
    ]
   }
  }
 }