How to Fetch Product Default Variant ID Using GraphQL in Shopify Theme App Extension

Shopify Apps
3

async function getDefaultVariant(productId) {
const shopifyStore = “my-store.com”;
const finalProductId = ‘gid://shopify/Product/’+ productId;
const query = query { product(id: "gid://shopify/Product/${productId}") { variants(first: 1) { edges { node { id } } } } };

const response = await fetch(https://${shopifyStore}/admin/api/2023-10/graphql.json, {
method: “POST”,
headers: {
“Content-Type”: “application/json”,
“X-Shopify-Access-Token”: ‘app-access-token’,
},
body: JSON.stringify({ query }),
});

const result = await response.json();
return result.data.product.variants.edges[0]?.node.id || null;
}

I am fetching the default variant ID of a product using the code below, but I am getting an authentication error. I am using this in a Theme App Extension Liquid file and obtaining the access token from my Shopify Partner account. Is the access token correct, or am I using the wrong one?