Switching upsell apps without leaving anything behind

September 18, 2026 · 2 min read

Changing upsell apps takes an afternoon, as long as you do it in the right order. In the wrong order you get a week with no offers at all, or two apps showing offers at once, or a discount code from the old app still working months later.

Before you uninstall anything

1. Write down your current offers: the products that trigger them, the products offered, the discounts, and which ones actually earn. Most apps can’t export them in a form another app can import.
2. Note your numbers for the last month or two — views, acceptances, revenue — so you have something to compare with.
3. Install the new app and rebuild your best offers, switched off for now.

The cart page

Two apps catching the checkout click at once is the classic mess: two pop-ups, or one blocking the other. Switch the new offer on only once the old one is off. In the theme editor, under App embeds, check that only one upsell app is enabled.

The post-purchase page

Only one app can use it. In Shopify, open Settings, then Checkout, and select the new app for the post-purchase page. Until you do, the old app keeps the slot even if its offers are paused, and the new one shows nothing.

Uninstall, then clean up

1. Uninstall the old app. Apps built on theme app extensions are removed from your theme automatically.
2. Older apps may have written code into your theme files. Search your theme code for the old app’s name, or ask its support what it added.
3. Open Discounts in Shopify. Apps that give a discount on an offer often create discount codes, and those can outlive the app. Deactivate or delete the ones you no longer use.
4. Check your next Shopify invoice to confirm the old app’s charges have stopped.

Compare fairly

The first weeks aren’t comparable with the old app’s history: new offers, a new layout, perhaps a different season. Give the new setup a full month before judging it, and compare the same measure — revenue per view, not totals.

Arriving at FlatUpsell, and leaving it

Rebuilding an offer in FlatUpsell takes a minute: the product that triggers it, the product to offer, the discount. The cart offer is a theme app extension, so uninstalling leaves nothing in your theme. One thing to know: when a cart offer carries a discount, FlatUpsell creates a discount code for it, named FU- followed by a number. Deleting the offer deletes its code, but uninstalling the app doesn’t, because Shopify cuts the app’s access at that moment. If you leave, delete your offers first, or remove the FU- codes from Discounts afterwards.