Questions · Buy

Why did the UCP checkout fail if my store works?

Because the endpoint is a separate route to purchase from your storefront. Agents call it directly, without loading a page, so it can fail while every page on the site works. On Shopify the platform runs it for you, which is why the fix is usually a support request to the platform rather than a change to your theme.

Why it happens

An agent platform that supports UCP reads the manifest at /.well-known/ucp, finds the shopping service and its endpoint, and calls it directly: search the catalogue, then create a checkout with the item, the buyer and the delivery address. No web page is involved, so a storefront that works in a browser says nothing about whether this route works.

Ottom makes those same calls with a synthetic buyer, reads what the store answers, and cancels the checkout. It never completes one and never submits payment. A failure counts against the store only when the endpoint itself failed: an error that is about who is calling, such as a rate limit, or a checkout that asks for more buyer details, is the protocol working.

It is reported at medium severity. The storefront checkout is graded on its own by the browser journey, and this is one channel failing rather than the store being unable to sell.

Run a free scan and find out which of these your store actually hits.