Just wondering if we building our own website that integrated with custom appointment and product, is possible to integration with customer login or create account function so we can keep record for return customers please?
Currently a customer login or account creation isn’t currently available with our APIs. We’re constantly working to improve our features based on feedback like this, so I’ll be sure to share your request to the API product team. 
Thanks Bryan, is possible to have customer login or create account on Square shopping site, then bring the customer ID and session data into our customised appointment booking site (same domain name), so we can create the order by using https://developer.squareup.com/explorer/square/orders-api/create-order ?
We currently don’t have customer accounts. Our accounts are seller accounts. Also customers are scoped to the merchant account. This means that the customer will have to be created on your account. Once created on your account you can then use the Square generate customer_id to create orders, bookings, or payments with.