Short answer: a product page can contain more than one form that adds the product to the cart: one behind the Add to cart button and another behind the Buy it now button. Pre-order terms travel with the order only if the pre-order choice is present in every one of those forms. If it is missing from one, that button places a normal order.
What you see as a merchant
A customer buys through the accelerated checkout button, and the order arrives without the pre-order terms: no deposit, no later balance, no ship date. The same product bought through Add to cart behaves correctly, so the problem can be missed in a quick test.
Why a theme renders more than one form
Some themes put the Buy it now button (the dynamic checkout button, rendered with Shopify's payment_button Liquid filter) in a separate product form from the Add to cart button. The pre-order choice has to be sent as the selling plan field in both. Pre-orders in Shopify are built on selling plans, which define the pricing, billing, delivery and inventory rules of the option (Shopify developer docs). Shopify's pre-order UX guidelines also treat the two buttons separately (Shopify developer docs: pre-order UX guidelines).
Why a script alone can miss it
An app script that adds the selling plan field only once, at load, can run before the accelerated checkout form exists in the page, because scripts in a block run while the page is still being parsed. A single sync at load misses a form that appears later. One approach is to write the selling plan into every form: on load, when the page changes, and when a button is clicked.
How to test your store
- Open the pre-order product page in a private window.
- Go to checkout once through Add to cart and once through Buy it now (you do not need to pay).
- On both checkouts, read the lines for what is due today and what is due later. If one path shows the full price today, that path skips your terms.
- Repeat with a second theme or after any theme update.
What stays outside the pre-order
Some limits come from Shopify, not from an app. Shopify's documentation lists payment providers that pre-orders support, and says pre-orders cannot be used through Shopify POS, on draft orders or with B2B, and do not support "Buy X get Y" discounts, cart permalinks or stores with checkouts customized through checkout.liquid (developer docs).
How Dropsoon handles it
Dropsoon adds the pre-order choice to every product form it finds, and checks again as the page changes and when a button is clicked, and labels the main button "Pre-order", which you can change. In our tests, a $100 product with a 30% deposit shows "Due today $30.00" and a later balance of $70.00 at checkout through both Add to cart and Buy it now. We have not tested every payment button a theme or browser can show, so run the test above on your own store.
Last checked: 14 October 2026. Sources: Shopify developer docs, pre-order UX guidelines.