Block checkout with a custom error message

Before you start

• Add the Rules Executor app block to your checkout and allow it to block checkout progress. How to add it.
• Know the condition you want to stop. For example, a shipping country you can’t ship to, a product that can’t ship with another, or a cart below a minimum total. Every condition.

Steps

1. In Checkout Ninja, open Rules and click New checkout rule (or Create a checkout rule if you have none yet).
2. Enter a Title, up to 30 characters. Buyers never see it.
3. Under Condition, click Add condition and set up the first condition. Add more if you need them.
4. Set Condition Match Type:
   • Only apply when All Conditions Pass to block only when every condition matches;
   • Only apply when Any Condition Passes to block when at least one matches.
5. Under Action, click Add Action and choose Show Error Message.
6. Choose a Position for the message. Use Top of the checkout unless the error is about one field.
7. Write the Message. Tell the buyer what to change, for example “We can’t deliver to PO boxes. Please enter a street address.”
8. Set Status to Active.
9. Click Save.

Example: block PO box addresses

• Condition: Shipping Address 1, operator Match regex ( Regular Expression), value [Pp]\.?\s*[Oo]\.?\s*[Bb][Oo][Xx]. This catches PO Box, P.O. Box and po box. The Contains operator is case-sensitive, so PO Box wouldn’t match po box.
• Action: Show Error Message, Position: Shipping Address 1.

Verify it worked

1. Open your checkout with a cart and address that match the rule. Try to continue. The message appears in the position you chose, and checkout doesn’t move forward.
2. Change the checkout so the rule no longer matches, for example edit the address. Try again. You can now continue.
3. Test a checkout that never matched the rule. It goes through with no message.

Limitations

• The block depends on permission. Shopify only lets the Rules Executor stop a buyer if you’ve allowed it to block checkout progress in the checkout editor.
• Shopify Plus only for the information, shipping and payment steps.
• The message is plain text. You can’t add links or formatting.
• The error is tied to the page where the Rules Executor sits. On three-page checkout, a buyer can reach later steps if the executor is only on an earlier one and the condition only starts matching later.

Troubleshooting

Buyers can continue even though the rule matches. The Rules Executor isn’t allowed to block checkout progress, or it isn’t on the page the buyer is on. Step-by-step fix.

The message never appears. Check the rule’s Status is Active, the Rules Executor is in your checkout, and your test checkout really matches the conditions. All versus Any is a common mix-up. Full checklist.

The message doesn’t show next to Email or Phone. Use Top of the checkout instead. The message still blocks the checkout, and the buyer sees it at the top.