How can I set up native checkout on my own domain?

[Xantey]

Hey guys, 

I already tried to get some informations from the support, but they couldnt help me unfortunately. 

I found an online shop (I have no clue if its okay to link them here), which are using a headless solution as it seems to me, because they dont have the url slugs (/pages/ etc). Their checkout is the native shopify one, but on their own domain. That would be the perfect fit for my project. But I dont get it, how they achieved that. If they are on their own hosted infrastructure with completely custom URLs, how is it possible the customer is not redirected to the shopify checkout domain? 

I hope someone can explain the approach to me, or give me a hint, thank you very much.  

Edit: After thinking more about a solution, I guess they are using a subdomain which is connected to shopify. So the checkout Domain is then 'checkout.yourdomain.com'.

Best regards