Open WeUpsell Dashboard
Start by logging into your Shopify admin panel and navigating to the WeUpsell Dashboard.
Go to Templates
Once you’re in the dashboard, find and click on the Templates section.
Click on the "Pre Purchase Upsell"
Click on Pre Purchase Upsell widget
Customize the Widget
Click on the product image to select the product you want to add on the checkout page.
You can also apply a discount if desired.
Note: This is a one-time offer and will not be available to the customer later.
You can change the offer timer
Save and Publish the Template
Click on Save and Exit to store your changes.
Click on Save and Publish to make the offer live.
Final Look:
Quick Note: You can add a trigger as "Popup trigger on add to cart" from Product Trigger settings of Display Conditions to popup this widget whenever user clicks on "Add to Cart" Button.