The short version

Shopify's own Buy again button in customer accounts puts the products from a past order straight into the cart. It skips the product page — and that is where your options live. So a customer could reorder a product and end up with none of the options you made required.

The app now provides its own Buy again button that handles this correctly. To use it you do two things: add the app's button, then turn Shopify's own button off.

Before you start

You need the new customer accounts. The app's button only works in Shopify's new customer accounts, not in the classic ones. If your customers still log in through the old account pages, this feature isn't available to you yet.

The app may ask for one new permission. Open the app. If you see a banner that says App update available with an item called Safe reordering in customer accounts, click Update app and accept it. Until you do, the app's button will not appear anywhere, even after you add it.

You need to be a store user who is allowed to install and manage apps.

Step 1. Add the app's Buy again button

1. In your Shopify admin, go to Settings → Checkout and click Edit.
2. At the top of the editor, open the page selector and switch it to Orders.
3. Click the Apps icon in the left toolbar.
4. Under APO Product Options, find APO Buy again and click the + next to it.
5. Choose Orders and Order status.
6. Click Save.

Step 2. Turn off Shopify's own Buy again button

Do this only after Step 1, so your customers are never left without a button at all.