I recorded you the video with all instructions ([url removed, login to view]). You also have pdf in attachment with little details.
We want to make 3 different upsells. First one is in cart, second in checkout and third one at "thank you" page.
We use Wordpress - Woocommerce system, and upsells should be build as plugins, work on more webshops and easy to use and change (example : Different products, different text etc.).
We are looking for developer that will solve all those 3 upsells together.