# Checkout validation: block orders

> Block checkout with your own error message when the cart, address or discounts break your rules, like PO boxes or minimum order.

Source: https://backtrackhq.com/docs/rules/checkout-validation/

"Validate checkout fields and show custom error messages." A
validation rule stops the shopper from completing checkout and tells
them why. For example, block PO Box addresses, or require a minimum
order amount.

> **Caution:** A validation rule can stop real orders. Always test it
> as a draft first.

## Before you start

- Write the error message you want shoppers to read. Say what is
  wrong and how to fix it.
- Decide between **Block** and **Allow**. **Allow** is an
  allow-list. It blocks every cart that does not match. See
  [Actions](#actions).

## Set it up

1. **Open Rules and click Create rule.**

   (Screenshot: The Rules page with the Create rule button)

2. **Under Validation, find Checkout validation and click Select.**

   (Screenshot: The Choose rule type page with the Checkout validation card)

   On the rule page, name the rule, or click **Start from a use case**.
   The name is for your reference only. See
   [Start from a use case](https://backtrackhq.com/docs/building-rules/use-cases/).

3. **Pick a rule set, set the timing and add your conditions.**

   In **Rule sets**, pick the set with the conditions you need. For
   example, discount conditions are in their own rule set. Under
   **Validation timing**, choose when Shopify checks the rule. Both
   options are on by default. See [Settings](#settings). Then add your
   conditions under **When at checkout**, for example **Has P.O. box
   address**. See
   [Conditions, groups and blocks](https://backtrackhq.com/docs/building-rules/conditions-and-groups/).

   (Screenshot: A validation rule block with a Has P.O. box address condition)

4. **Pick Block or Allow, then add the error message.**

   Under **Error Message Configuration**, pick an **Error message
   position** and type the **Error message**. Use **Add error message
   configuration** to show the message in more than one place.

   (Screenshot: The validation action with an error message row)

5. **Save it as a draft, test it, then activate it.**

   In the **Status** card, choose **Draft** and save. Then go to
   checkout on your store and enter the [test email](https://backtrackhq.com/docs/get-started/test-before-going-live/) from the rule's **Status** card.
   Only this email sees a draft rule. Try a cart that should be blocked and one that should pass. Check that the message shows where you chose.

   (Screenshot: The Status card set to Draft with the test email hint)

   When it works, choose **Activate** in the **Status** card and save.

## Actions

### Block customer from completing checkout

Blocks checkout when the conditions **match**. Everything else can
check out.

Example: conditions "Has P.O. box address". Result: carts shipping to
a PO Box are blocked. All other carts pass.

### Allow customer to complete checkout

An allow-list. Checkout is allowed only when the conditions
**match**. Every cart that does **not** match is blocked and sees
your error message.

Example: conditions "Country code has any of these values: United
States". Result: US addresses can check out. Every other country is
blocked.

> **Caution:** **Allow** never just "lets something through". It
> blocks everything that does not match. If you only want to stop one
> case, use **Block**.

## Settings

(Screenshot: The Checkout validation rule page with its settings cards)

### Error message position

Where the error shows at checkout.

Options: Top of the checkout page, or below one of the input fields:
Country, Email, Customer phone number, Shipping phone number,
Company, Address line one, Address line two, City, Province, Zip
code, First name, Last name.

### Error message

The text shoppers see. It has a **Translate** button for other
languages. See
[Translate shopper messages](https://backtrackhq.com/docs/building-rules/translate-messages/).

### Validation timing

When Shopify runs the check. Pick at least one. Both are on by
default.

- **When interacting with checkout:** "Validate when customers fill
  fields, make selections, or interact with checkout elements".
- **When completing checkout:** "Validate when customer attempts to
  submit and complete the checkout".

### Allow customers to complete checkout

In the **Settings** card, under "If the app fails or experiences a
problem:". This setting only matters if the app itself fails or times
out at checkout. It does not change how the rule works the rest of
the time. Your conditions still allow checkout or show your error
message.

- **Ticked (default):** customers can complete checkout without
  validation. The help text says "All orders will be processed
  without validation".
- **Unticked:** checkout is blocked until the app responds.

### Status

Options: Draft, Activate, Deactivate.

## Examples

Open **Start from a use case** on the rule page and pick one of these:

- **Block PO Box addresses:** prevents checkout with PO Box delivery
  addresses. See
  [Example: block PO box addresses](https://backtrackhq.com/docs/rules/example-block-po-boxes/).
- **Require minimum order amount:** blocks checkout below a minimum
  cart value.
- **Restrict checkout to domestic orders:** allows checkout only for
  addresses in your store's country.

For discount codes, see
[Example: block discount codes](https://backtrackhq.com/docs/rules/example-block-discount-codes/).

## Limits

The **Limitations** card on the rule page lists: "Validation rules
don't support draft orders." In Shopify, validation rules also run on
draft orders. See [Limits](https://backtrackhq.com/docs/rules/limits/#draft-orders).

Conditions marked "(Plus required)" need checkout extensibility, which
means Shopify Plus or a development store. They don't match in
accelerated checkouts such as Apple Pay or Google Pay. See
[Limits](https://backtrackhq.com/docs/rules/limits/).