Blocking at checkout is safe but late — the customer has already built a cart they cannot buy. Locking the quantity picker stops the problem at the product page.
Before you start
- The Premium plan.
- The theme app embed enabled and saved — install.
- Which products need it, and what the value should be.
The three metafield types
| Type | Effect on the quantity input |
|---|---|
multiple_of | min and step both become your value — quantities step 6, 12, 18 |
min_quantity | min becomes your value |
max_quantity | max becomes your value |
Steps
1. Install Nex Validator
Search Nex Validator in the Shopify App Store, or use the button below. Approve the permissions and the app appears in your admin under Apps. There is a free trial, and it works on every Shopify plan.
2. Enable the theme app embed if you have not already, and Save the theme.
Screenshot coming soon
The app embed switched on in the Shopify theme editor
3. Set the rule metafield on each product, with the type and value you need. Use Shopify’s bulk editor or a CSV import rather than editing products one at a time.
Screenshot coming soon
The rule metafield set on a product in the Shopify admin
4. In the app, open or create a rule and turn on Allow bulk limit.
Screenshot coming soon
The Allow bulk limit toggle enabled in the rule form
5. Save with Status set to Enabled.
Verify it worked
- Open a product with the metafield. The quantity input should refuse invalid numbers — stepping in your multiple, or refusing to go below the minimum.
- Open a product without it. The input should behave normally.
- Force an invalid quantity anyway (edit the cart, or use a direct link) and confirm checkout still blocks. If it does not, the storefront lock is your only defence and it is bypassable.
If your theme does not respond
Themes render quantity inputs and cart drawers differently, and some need pointing at the right elements. The app exposes selector overrides for exactly this — see showing the message on the cart page, which covers the same settings.
Start by confirming the embed is enabled and the theme is saved; a preview session does not count.