How to resolve event loop error in app proxy ?

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Topic summary

Author is building a Shopify app extension to compute shipping discounts, calling an external API via the app proxy. When triggering the call with a JavaScript Promise inside the extension, they hit a runtime error:

  • “Pending jobs in the event queue. Scheduling events is not supported when the experimental_event_loop cargo feature is disabled.”

Context: App proxy is configured per Shopify docs; the error appears specifically when using a Promise to initiate the API request. The message indicates the runtime environment forbids scheduling event-loop tasks (e.g., async operations), likely due to the disabled experimental event loop.

Key terms: App proxy routes storefront requests to an external app server; Promise is a JavaScript construct for asynchronous operations.

Ask: Guidance on the cause of this event-loop restriction and how to resolve or work around it when making external API calls.

Status: No solutions provided yet; issue remains unresolved.

Summarized with AI on December 16. AI used: gpt-5.
1

I’m working on a custom Shopify app extension that calculates shipping discounts by making an external API call using the app proxy. I’ve set up the app proxy according to the documentation, but when I use a Promise to trigger the API call within my extension, I’m encountering the following error :

Pending jobs in the event queue.
Scheduling events is not supported when the 
experimental_event_loop cargo feature is disabled.  

I’ve searched for solutions but haven’t found any relevant information addressing this issue. Could anyone provide guidance or insight into what might be causing this error and how to resolve it?