I have a Shopify Checkout UI Extension that is functioning correctly in production for most users. The extension uses the Buyer Journey Intercept to trigger a backend validation call (a direct backend API call, not a proxy route) during checkout, and this flow works as expected across multiple browsers.
However, I have observed that for some users—specifically those using the Safari browser—the Buyer Journey Intercept does not appear to execute at all. In these cases:
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No network request is made from the extension to my backend
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No validation logic is triggered
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The checkout flow proceeds without invoking the intercept logic
The same users and carts behave correctly on other browsers (e.g., Chrome), and the backend endpoint itself is stable and reachable.
I am trying to understand:
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Why the Buyer Journey Intercept may not execute for Safari users
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Whether this is related to Safari-specific behaviors (e.g., Intelligent Tracking Prevention, third-party request blocking, or browser security policies)
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Whether there are Shopify Checkout UI Extension constraints or known limitations affecting Safari
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What the recommended and reliable resolution is to ensure consistent execution across all browsers
Any guidance on debugging strategies or architectural changes to make this flow Safari-safe would be appreciated.