Minimal Setup

<head>  <script type="module" src="https://cdn2.circuly.io/v1/1.8/cart.js"></script>  <script src="main.js" defer></script></head><body>  <button onclick="addProductToCart()">add product</button>  <div data-embed="basket">    <script type="application/json">      {        "api_key": String      }    </script>  </div>  <div id="circuly-cart"></div></body>
// main.jslet addProductEvent = new CustomEvent("circuly-add-to-content", {  detail: {    sku: String,    /* Optional key-value pairs */    quantity: Number,    subscription: Boolean,    subscription_end: [String, null],    subscription_interval: [Number, null],    subscription_period: [String, null],    subscription_start: [String, null],    subscription_type: [String, null],  },});function addProductToCart() {  dispatchEvent(addProductEvent);}