For discussing the development and integration of subscription-enabled shops using Shopify's Subscription APIs.
https://shopify.dev/apps/subscriptions/app-extensions/getting-started
The docs state you can provide shopify extension serve with a reference URL. This URL is incorrect.
shopify extension serve --resourceUrl="/product/12345"
This leads to a 404. Instead it should be:
shopify extension serve --resourceUrl="/products/12345"
Thank you for reporting this typo ! It will be fixed in an upcoming documentation release !
To learn more visit the Shopify Help Center or the Community Blog.