You can use the same column layout as the admin customer list CSV import ( download sample CSV ).

Your CSV must include columns for all of the following (header names can be either form):

• Email or email_address
• Phone or phone_number
• First name or first_name
• Last name or last_name

You can optionally supply these headers:

• Short Name, shortname, or short_name
• Phone country or phone_country (eg. "us", "gb", "au"...)

Example (legacy optin column names):