These limitations come from Shopify’s Cart and Checkout Validation system. They are Shopify platform limitations, not limits created by Nex Validator.
Where validation runs
| Where the customer orders | Validation works? |
|---|---|
| Online store cart | Yes |
| Custom storefronts using Shopify’s Storefront API cart | Yes |
| Checkout | Yes |
| Express checkouts — Shop Pay, PayPal, Google Pay, Apple Pay | Yes |
| Shopify POS | No |
It cannot be bypassed
Checkout validation runs on Shopify’s servers, so customers cannot avoid the rule by going directly to checkout. See Shopify checkout validation for what the app enforces.
The storefront quantity lock is different. It helps prevent customers from choosing an invalid quantity while shopping, but checkout validation is the final check before the order can continue.
The 25-function ceiling
Shopify allows up to 25 active validation functions per store. This total can include validation functions created by other installed apps, not only Nex Validator. See Limits for more details.
Where error messages surface
Validation messages always appear when the rule blocks checkout. Showing the same message in the cart can depend on how your Shopify theme displays its cart.
If the message appears at checkout but not in the cart or cart drawer, check the Show the message on the cart page setup and make sure the app embed is enabled.
Not supported in POS
Nex Validator checkout validation does not run in Shopify POS. These order-limit rules apply to supported online checkout flows, not in-person POS orders.
Sources
Shopify revises these APIs periodically. Verified against the above in August 2026.