I am developing a headless Shopify Shop using Nextjs and React for the Frontend. I have built pretty much the whole store but I have so far been unable to build a custom headless checkout page because there is a plethora of conflicting, incomplete and incorrect information on that topic. I have now read people saying that you can use either the Storefront API, the Admin API with a custom sales channel, the Admin API alone, the Checkout API with a custom sales channel, the Checkout API alone or even the JS Buy SDK (which makes the least sense to me). Some people also say it is not possible at all and that you absolutely HAVE to redirect to a shopify domain, but I looked at all the Headless Shopify stores Shopify itself promotes and uses as references for headless stores on this page:
https://www.shopify.com/plus/solutions/headless-commerce
and these are the stores:
https://www.allbirds.eu/
https://grassrootscoop.com/
https://www.babylist.com/
https://www.wearfigs.com/
so I assume they are 100% positively Headless or Shopify is straight up lying. They ALL use a custom checkout either on the exact same domain as the rest of the store or on subdomain and NONE of them redirects the user to a different domain on checkout. Can now anyone give me a definite and most importantly CORRECT answer on how I can create a checkout page which will be located on the same domain the rest of my headless store or on a subdomain? If I would need to redirect the user from the domain of my Headless store to a Shopify owned domain to check out this will be absolutely positively make me change to a another technology for good.
