Why is variable/variation product not purchased properly using custom upsell page?

I’ve been testing different methods of showing the variable product in the upsell with no luck. The variations appear on the front end, but no matter what I select, the order doesn’t show the variant of the product, just the parent. In addition, it also charges the customer the base amount (lowest of the variants), instead of the actual variant price. I’m using the variant selector shortcode on a custom page.

Probably it happens because you are using 
the yes/no shortcodes in inserted mode like
that:

<a href="[wc_1cu_yes]">YES</a>

But should be like this:

[wc_1cu_yes]YES[/wc_1cu_yes]

Or instead your custom link or button should have
additional CSS class "wc_1cu_custom_offer_accept" to 
transfer the variable data properly.