Montreal-based Shopify experts cooking some Shopify apps.
The apps runs on load and looks for all upsells that should be rendered ( matches cart rule/location rule or there is manual snippet present)
If you want to be able to show upsell later , on specific event, you have to follow the logic:
1) On initial run there shouldn't be a snippet for upsell
2) On event that you want to fire the upsell you should a) append the upsell snippet code to your store html (in any place in case of popup) by calling the following (or something similar):
$('selector').append(<div class="tabarnapp_upsell" data-id="your_upsell_id"></div>)
b) Rerun app logic by calling window.Ultimate_Upsell.run:
Tabarnapp's mission is to help you get the most of each visit on your Shopify store.