ShopifyBuy js API returning 404

[manifesto]

I am trying to debug a 404 issue for a product using the ShopifyBuy client api. The product is always returning 404 and I am unable to understand why.

The code below is where the issue is happening. The variable productId has a valid id for an active product in the Shopify store but client.fetchProduct returns 404. 

var productId = productDiv.data("shopify-id");
client.fetchProduct(productId).then(function (fetchedProduct) {
   productDiv.data("product", fetchedProduct);
});

Request URL: https://shop.mysite.co/api/apps/6/product_listings/[productId]

Has anyone seen this issue before? 

Thanks