Pre-Checkout Upsell is displayed on the Checkout page when the visitor or user clicks on the Proceed to Checkout button.
This helps you to Upsell an offer before even the user has reached the Checkout page.
How to Setup Pre-Checkout Upsell in CartFlows?
Navigate to CartFlows ( WordPress Dashboard ) > Flows > your_flow > Edit the Checkout Page -> Navigate to Checkout Offer tab -> enable the Enable Checkout Offer option > select your product under Select Product option.
You can also change the other options/setting in the checkout offer below for further customizations.
Visit the Checkout Page on the frontend. After filling the details there, now when you click on Proceed to Checkout an offer popup will be displayed.
Like the following screenshot –
Note: It will work with almost all WooCommerce payment gateways.