I am following the official Shopify Agents checkout tutorial, including authentication, product search, cart creation, and then invoking create_checkout on the discovered UCP MCP endpoint from getMcpEndpoint(origin). Cart creation works, but create_checkout returns AuthenticationFailed with Missing …

Hi @Alan_G . I managed to solve this by adding Shopify-Buyer-IP header in POST request to the merchant’s UCP endpoint.

Hey @Milan_Jakara - thanks for getting in touch. Would you happen to have the request ID from the response headers for the checkout creation call on hand? Happy to look into our logs and see if I can assist here - hope to hear from you soon!

Glad to hear you figured this out @Milan_Jakara ! Let us know if you run into any other issues :slight_smile:

i had same issue, and i resolved it with the header in POST, but i hit now this: Internal error calling tool create_checkout: Core client error i put the correct json body with the id of ProductVariant and buyer info, but i get this error above, same error i get with the create_ca…

Hi @Saba . You need to provide ‘Shopify-Buyer-IP’ header in the request.

Hi @Milan_Jakara . Thanks for sharing this, I tried this and the error persists. Looks like buyer info is required for “create_checkout”, I am getting this error on “create_cart”. Could this be related to my store being password protected (?) as it’s not happening on public stores.

Checkout MCP create_checkout fails with “Missing required buyer IP header” despite following official demo

Agentic Commerce

Gil-Shopify October 9, 2026, 5:04pm 9

Hey everyone. We’ve added documentation that now covers the buyer IP requirement: Auth and rate limiting

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Checkout MCP create_checkout fails with “Missing required buyer IP header” despite following official demo

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