Hi, we have a headless implementation of Shopify with our own agency CMS. The client has moved up onto Plus so we can implement multipass and allow customer accounts on the front end which provide a logged in experience at the checkout.
The issue we face is that even with the multipass access token this doesn't log the user in at the checkout, it simply pre-fills the email address for the user.
What is the correct process for this? The API documentation seems to suggest the multipass token is for amending the customer's data but not to provide Shopify with a link between the headless cart and the Shopify hosted checkout.