What the external product URL field is
External product URL is a product-level field on Shopify Agentic-plan stores that points to the canonical product page on the merchant's existing (non-Shopify) storefront. It's how the AI channel deep-links a product card back to where the merchant actually wants the buyer to land. Full Shopify online-store plans don't have it because they use the Shopify-hosted product URL automatically.
When the field is required
Only on Agentic-plan stores. The Catalog requirements page lists it as a sub-clause under the products-published-to-channels gate: 'Agentic plan users must include external product URL.' Stores on Basic / Shopify / Advanced / Plus plans use the Shopify-hosted product URL automatically and don't see this field.
What happens if it's missing on Agentic-plan products
Catalog eligibility fails for that product. The product won't be syndicated to AI channels because the AI channel has no canonical URL to deep-link to. In ChatGPT (referrer model) the lack of a destination URL is fatal — the channel can't surface the product card without somewhere to send the buyer. In Copilot / Gemini / Perplexity / Shop (direct-checkout channels), the in-chat checkout could theoretically complete without the external URL, but Shopify still requires the field because the channel may want to surface the product card with a 'View on merchant's site' link.
Field-setting checklist
Walk these five steps when setting up an Agentic-plan store. The field is per-product, so a bulk approach is necessary at any non-trivial catalog size. Most Agentic-plan stores use a CSV import with the external URL column mapped, or an API-driven sync from their existing PIM.