When I do exactly the same, but not as a guest, it works. That means I register with the same body data besides „guest“: true (which I deleted in the body).
Any suggestions what might be wrong, when registering as a guest.
I’m replying to this topic, because I had the same problem, and so it might be useful for people who find this forum post in the future.
A guest can’t be logged in BUT if you make the API-requests in the right order, the guest will count as „logged-in“ upon registration for the checkout step.
The right order here means creating a cart before registering a guest: (only listing the API endpoints)
/store-api/context – use this token until step (5)
/store-api/checkout/cart
/store-api/checkout/cart/line-item
/store-api/account/register – the response header will contain a new sw-context-token