Cart Validation API not running properly?

Technical Q&A

Topic summary

A developer has implemented a JavaScript cart validation script within their Shopify app to prevent quantity modifications for specific products (allowing only deletions). While testing shows the script works correctly across different shops, some end customers are reportedly still able to change quantities despite the validation being in place.

The developer has checked app logs in the Shopify Partner Dashboard and found no errors—everything appears to be functioning normally. They are seeking information about potential ways the cart validation mechanism could be bypassed outside of POS (Point of Sale) systems.

The issue is causing client dissatisfaction, and the developer is looking for help identifying the root cause or any known workarounds that might explain this inconsistent behavior.

Summarized with AI on October 29. AI used: claude-sonnet-4-5-20250929.
1

Hello,

I’ve developed an app that relies on the quantity of line items remaining unchanged (only deletions are allowed).

To ensure this, I implemented a cart validation script in JavaScript and deployed it within the app to prevent users from modifying the quantity of specific products.

In my tests across different shops, the script works correctly in all scenarios.

However, some clients have reported that a few of their customers are still able to change the quantity despite the validation.

I checked the app logs in the Shopify Partner Dashboard and found no errors, everything appears to be running as expected.

Is there any known way to bypass the cart validation mechanism outside of POS?

I would really appreciate any help, as a few of my clients are quite upset about this issue.

Thank you very much!