It depends on Client Config > Business: General > "Need login to access website":

• Only Registered Users: any ordering page redirects to Login immediately.
• Allow Guest (default): customers can browse and add items to the cart without logging in.

Either way, placing the actual order always requires a logged-in account when guest access is off — reaching the Delivery/Payment step without one shows a Login screen instead of the payment form, and the server-side "complete checkout" call itself is refused for a logged-out session in that case.