The customer pays the difference themselves, on Shopify's own secure payment page, after seeing the exact amount. Tacey never charges a card on its own. Until they pay, the order is held so it does not ship unpaid.
Which changes can cost more
Adding a product, with Add a product to your order or Recommended for you.
Increasing a quantity, with Change product options.
Swapping to a more expensive product, with Replace product.
Upgrading to faster shipping, with Upgrade shipping method.
Occasionally, a new delivery address that costs more tax or shipping.
What the customer sees
They choose their change.
Before anything is saved, they see Payment due with the amount, and the note "Shopify's own calculated total, including tax." Tacey does not work this figure out itself. It is Shopify's number, in the currency the customer paid in.
They press Confirm & pay. If the amount Shopify calculates has moved since they were shown it, the change is refused and they are asked to look again, so they can never pay a figure they did not see.
The order is updated, and they get a Pay now button that opens Shopify's own payment page for the difference.
Once they pay, the order is settled.
Shopify's own "your order was changed" email is not sent at this point, because the customer is paying on the page in front of them.
If they close the page without paying
The change has been made, but the money has not arrived. That is a real unpaid balance, not an error, and Tacey treats it as one:
The order is held. Tacey places a hold on fulfillment in Shopify so it cannot ship unpaid.
The order is tagged tacey-payment-owed, so you can find it in your Shopify order list.
The ledger says so plainly: Payment not completed yet.
If they pay later
Tacey sees the payment, releases the hold, removes the tag, and records the amount as paid in the ledger. You do not need to do anything.
If they never pay
Each tool has a waiting time, 24 hours unless you change it:
Hours to wait for payment on an added item, on the Change product options settings page, covers item changes and most other tools.
Hours to wait for payment on an upgrade, on the Upgrade shipping method settings page, covers shipping upgrades.
When the time runs out:
If the unpaid change was a product the customer added, Tacey takes it back off the order, so an item nobody paid for does not ship.
The hold is released, so the order is never stuck.
The ledger records Payment was never completed.
The tacey-payment-owed tag stays on, so you can follow up if you want to. If the customer pays after all, Tacey still records it.
What this does NOT do
It never charges a saved card. The customer always completes the payment themselves.
It never works out tax or shipping on its own. Every amount comes from Shopify.
It does not email the customer a reminder to pay. The Pay now button is on their order page. If you want to chase a payment, contact the customer yourself.
It does not include this money in "Added after checkout" until the payment has actually been confirmed.
Frequently asked
Is the order changed before the customer pays?
Yes. Shopify applies the change and records the balance due. That is why Tacey holds fulfillment until the balance is paid or the waiting time ends.
Where do I see money collected this way?
In the ledger with the Money filter set to Added after checkout, and in the Added after checkout card on Home.
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