Shopify does not charge a customer automatically when an order gets bigger. So when a customer adds a product through Add a product or Recommended for you, Tacey shows them the exact amount, collects it through Shopify's own payment page, and keeps the order from shipping until it is paid.
Step 1: the customer sees the amount first
Before anything changes on the order, Tacey asks Shopify to price the change: the item, any discount, any shipping charge, and tax. The customer sees that figure, labelled as Shopify's own calculated total, with Confirm & pay and Back. Nothing has been charged at this point.
When the customer confirms, Tacey prices the change again and compares it with what they were shown. If the two differ (for example, a price changed in the meantime), the add is refused rather than charging an amount the customer did not see.
Tax on stores that add tax on top of prices. On some of these stores Shopify only adds tax to the new line once the change is saved. The figure the customer confirms can then read "+ tax", and Shopify's payment page shows the exact total before they pay.
Step 2: the item is added and the order is held
After Confirm & pay, the item is added to the order as a new line. If money is owed:
the customer sees Payment due and a Pay now button,
Pay now opens Shopify's own payment page for the difference, in the currency the customer paid in,
the order gets a hold on fulfilment and the `tacey-payment-owed` tag, so it does not ship before the balance is paid.
If nothing is owed, the customer sees "Nothing further is owed." and there is no hold.
Tacey does not send Shopify's "your order was updated" email for this change, because the customer is already on the page watching it happen.
Step 3: the customer pays
When Shopify records the payment, Tacey releases the hold, removes the tag, and marks the change as paid in your Ledger. The order then ships as normal with the new item in the same box.
If the customer adds a second item before paying for the first, both amounts fold into the one balance Shopify shows as owed on the order.
If the customer never pays
Tacey waits for the time set in Hours to wait for payment on an added item, found in the Change product options tool. The default is 24 hours; you can set anything from 1 to 168.
When the time runs out without a payment:
Tacey checks Shopify once more, right before acting. If the payment has just arrived, nothing is removed.
Otherwise, it takes the unpaid item back off the order and restocks it. No money moves, because none was collected.
It leaves a note on the order: "Tacey removed a product the customer added but never paid for (payment window expired). No money moved."
It releases the hold so the rest of the order can ship.
If the item cannot be removed cleanly (for example, you already changed or fulfilled it), the hold is still released so the order is never stuck. The item then stays on the order unpaid, so check the order and your Ledger and sort it out by hand. ## What this does NOT do
It does not charge a saved card. The customer always pays on Shopify's payment page.
It does not ship an unpaid add. The order waits, and an unpaid added item is removed before the hold is released.
It does not calculate prices itself. Every amount is Shopify's own figure.
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