A product a customer adds after checkout has to ship with the rest of the order. Three settings on Add a product, plus a few built-in checks, make sure customers can only add what you can actually send.
Hide out-of-stock products
Default: on. Products with no option in stock are dropped from the search results entirely, so customers never scroll past things they cannot buy.
Turned off, those products appear in the results, but an option that cannot be sold shows "This option is currently out of stock." and cannot be picked. Turning this off never lets a customer add an item you cannot sell; it only changes whether they see it.
How Tacey decides "in stock"
Tacey follows your own Shopify inventory settings for each option:
Not tracked in Shopify: always available.
Tracked, with "Continue selling when out of stock": always available.
Tracked, without it: available only while the quantity asked for is in stock.
This check runs again at the moment the customer confirms, using a fresh read from Shopify, so an item that sold out a second ago is refused rather than oversold. Add a product always respects these settings; there is no switch to ignore them.
Maximum quantity per add
Default: 5. Any value from 1 to 20. This is the most of one item a customer may add in a single request. A customer who wants more can add again, and each add is its own line on the order.
Locations an added item may ship from
Default: none chosen, which lets Shopify use its usual default location for the new line.
Pick one or more locations to restrict where an added item can be fulfilled from:
In Tacey, open Editing Tools, click Set up tools on the Thank you page card, and click Set up next to Add a product to your order.
Under Locations an added item may ship from, pick the locations.
Click Save.
With locations chosen, stock is counted per location. For a tracked item that cannot oversell, Tacey uses the first location in your list that has enough stock for the quantity asked for. If none does, the add is refused as out of stock. For an item that is not tracked, or that can oversell, the first location in your list is used.
Markets and availability
Every product a customer can add must be:
Active in Shopify (never Draft or Archived),
published to the customer's market, judged by the order's shipping country, or the billing country if there is no shipping address,
available for sale, and priced for that market.
A product your store does not sell in the customer's country never appears in their search and is refused if requested directly. An option that is not for sale shows as sold out and cannot be picked. None of this can be switched off, because offering something a customer cannot buy only creates a refund later.
What this does NOT do
It does not reserve stock while the customer browses. Nothing is held until they confirm; from then on the item is on the order and Shopify's normal inventory handling applies.
It does not split one add across several locations. One location fulfils the whole quantity of that add.
It does not check shipping rates for the new item. The item joins the existing shipment; no shipping line is added.
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