When you create a manual order or import multiple orders via CSV, ShipStation creates a customer record if you include specific information. If you do not specify this information, a customer record will not be created.
Make sure you include a unique email address in the email address field if you want ShipStation to create a customer record.
CSV Order Imports
ShipStation will only create a customer record if a username is defined.
Make sure that you specify a unique username for each customer or map the Email Address column on your spreadsheet into both the Username and Buyer Email fields.
This is how the customer record will appear in the Customers tab.