Store settings has a new Custom domain page. Enter an address you own, such as shop.example.com, and Magpie shows the DNS records to add where you manage your domain. If Magpie already hosts your DNS, it can add them for you.
Magpie checks the address every few minutes, says what is still missing, and gets a security certificate once the records are found. Products, collections, the cart and checkout then work at your address, and customers who pay come back to it. Your Magpie address keeps working too.