The ID returned from the API is the developer product ID, the shopId is a shop id, very similar to universe IDs, but useless. Right now, there is currently no way to get a product ID from a developer product ID (unless you search all pages of https://api.roblox.com/developerproducts/list?placeId={placeId}&page={page} and match the developer product ID with the product ID).
The website shows the actual product ID of the developer product (see here)