How to build single page sales page with checkout which ties into shopify? is this ever possible?

I am trying to build something like the link below that will tie purchaser into my existing shopify site once they purchase.

I see a lot of these style of checkout/sales pages but can’t see what people are using to build them.

https://offer.getakemiglow.com/offer/1/checkout-now.php?package=1&test=yes