Block add to cart at your threshold

Your threshold holds back a number of units so you never sell your last stock. Without the add to cart block, nothing tells the shopper that until later. With 12 in stock and a threshold of 5, a shopper can pick 10, add it, and only find out at checkout that 7 was the limit.

The add to cart block fixes that on the product page. It caps the quantity box at what is still buyable, and if a shopper still tries to go over it stops the add and shows your message instead. Nothing is sent to Shopify, so there is no error to recover from.

It also stops the Check out button

A shopper can end up over your threshold without adding anything: they put two in the cart when three were free, someone else buys one, and now the cart is over the line. Nothing they did changed, but the cart did.

So the block covers the cart too. When a shopper presses Check out with a line that is over your threshold, they stay on the page and your message appears under the button. They can lower the quantity or remove the line and carry on. This works on the cart page and in cart drawers, on every plan.

The quantity box in the cart carries the limit too

A shopper can change a quantity in the cart without ever going back to the product page, so the limit is on the box there as well.

• A protected cart line's quantity box is capped at what is still orderable, so the plus button stops where your buffer starts.
• Push past it - press plus at the cap, or type a bigger number - and your "Over the limit" message appears on that line, with the number they can actually take.
• A line with nothing left to order says so as soon as the page loads, in your "Item fully reserved" wording.
• A line that sits exactly at the limit says nothing. That is a correct cart, and there is nothing to tell the shopper off about.

This works on the cart page and in cart drawers, on every plan. Themes that do not label their cart quantity boxes in a way we can read get no cap and no message on the line. Those carts are still stopped at Check out.

Why shoppers should not see a plain error page

If a shopper got all the way to Shopify with a cart over your threshold, Shopify used to answer with its own error page: a white page reading "Something went wrong", with none of your branding. No app can restyle or redirect that page, and no theme can catch it.

Easy Stock Buffer now holds its message back until the checkout exists, so there is nothing left for Shopify to refuse a cart over. Inside the checkout the same message shows as a proper banner at the top of the page, in your wording. That page belongs to Shopify, not to us, so we will not promise it can never render again - what we can do is give it no reason to, and tell the shopper on the product page, on the cart line and at the Check out button long before they get there.

Turn it on

1. In Easy Stock Buffer, open the dashboard and find the setup steps.
2. Choose Open theme editor.
3. In the theme editor, open App embeds in the left sidebar and switch on Easy Stock Buffer.
4. Save the theme.
5. Back in Easy Stock Buffer, choose Check again. The step turns green once we can see the block on one of your product pages.

If the check cannot find it, it will say why: the embed is not switched on, your store is still password protected, or you have no products published yet.

What shoppers see

When a shopper asks for more than is left above your threshold, the quantity drops to what they can buy and a short line appears next to the button. When there is nothing left above your threshold, the add is stopped outright.

The wording is the one you already wrote. It comes from Settings, then Customer messages, where three messages cover every case: "Over the limit", "Item fully reserved", and the one shown when two or more items are blocked at once. Edit them once and they change in all four places a shopper can meet your threshold - next to the add to cart button, on the cart line, under the Check out button, and in the banner at checkout. There is no separate product-page wording to keep in step.

On Pro, you can also grey the button out and relabel it as sold out, so a fully reserved variant looks unavailable rather than merely refusing.

Turning it off

Under Settings, then Customer messages, switch off Block add to cart at your threshold. That switches off all of it: the block on the product page, the quantity cap there, the quantity cap and the message on cart lines, and the stop on the Check out button. The stock details it works from stop being written into your pages too, so nothing of it is left running. Shoppers can then build whatever cart they like and are stopped at checkout instead, with your message as a banner there.

The Pro sold-out look is a separate choice on the same page and keeps working either way.

What it does not cover

• Quick add buttons on collection and search pages. Those pages do not carry the stock numbers, so the add goes through and checkout catches it.
• Buy it now, Shop Pay, Apple Pay and Google Pay. Shopify builds those buttons in a way apps cannot reach. Checkout still blocks them, with your message. On Pro you can hide them for fully reserved variants.
• Shoppers with JavaScript switched off. Rare, and checkout still blocks.
• Two shoppers buying the last unit at the same time. No storefront can know what someone else is about to do. Whoever is second is stopped at checkout with your message.
• Headless and custom storefronts. A storefront built on Shopify's Storefront API runs no theme code, so an over-limit line can be added to the cart there. It is stopped at checkout.
• Very large carts and very large products. This reads up to 250 cart lines and the first 250 variants of a product. Past those points there is no cap and no message, and checkout is what stops the order.
• Themes whose cart we cannot read. The cap and the line message need the theme to label its cart quantity boxes in one of the ways Shopify puts in the page. Where a box cannot be matched, that line gets no cap and no message. The Check out button is still stopped.
• A typed quantity in the cart. The cap stops the plus button, not someone typing a bigger number. They get your message on that line instead, and Check out is stopped.

In every one of these the checkout block does its job, which is why both are worth having on.