Quick answer
If checkout validation is not blocking progress, confirm whether the rule is built as a Checkout UI Extension warning or as a Shopify Function validation, and confirm that block_progress is enabled when the extension is expected to block the buyer's progress.
Start with the rule
Ask what needs to happen. Should the buyer see a helpful warning, or should checkout be impossible until a rule is satisfied? Those are different requirements.
Check 1: Extension capability
Shopify's checkout extension documentation states that block_progress allows an extension to block the buyer's progress. If the extension needs to stop checkout progress and the capability is missing, the behavior will not match the requirement.
Check 2: Target and buyer journey
Make sure the extension is rendering on the checkout step where the rule needs to run. A validation that appears too late or in the wrong target can create a confusing customer experience.
Check 3: Client-side vs server-side
Shopify Functions can create cart and checkout validation rules that run on Shopify's servers and block checkout when business rules are not met. For rules that protect the business, server-side validation may be more appropriate than only relying on UI behavior.
Check 4: Test express checkout paths
Do not test only the normal checkout button. Express and accelerated checkout paths can behave differently depending on the extension and rule. A rule that appears to work in one path might not protect every path.
Fix path
- Define whether the requirement is warning or enforcement.
- Check the extension configuration for block_progress.
- Confirm the extension target and checkout step.
- Use Shopify Functions validation for rules that must be enforced server-side.
- Test normal checkout, mobile checkout, and express checkout paths.
Common misunderstanding
A disabled button is not a complete validation strategy
Front-end blocking can improve the user experience, but critical business rules should be enforced in a place the customer cannot bypass.