The only requirement is to have the user’s email address.

  1. Click on the top corner (profile icon), then click the “Invite a Team Member” link:

    https://lh3.googleusercontent.com/ZNcMduqMsUR3qqKM4BNWLMjalJ7_3bV8gCUm9UTBdgyRn3sjD1zrhjTNDUEKHyxPSS0yVwkBkJ-mob5IgZlzG2Fh-Dw8D1oRjvWL1uOSJjTnOfK6ogyNjUbeztjbrIm9j2ijWiq-

  2. To invite a new user to the Company, simply enter their email address in the “Email address” box and click the “Send Invitation” button. This will send an email to the user, with a link to activate their account and join the Company’s team.

    https://lh3.googleusercontent.com/KvmohaRDqjoNb24ArEk0UwgUQJ1WwauGk9ss5mAJLpPaX9OwJXk-s-SkR1INrLN23Q9BcYU7R7JpZYLPxF_WGZgusx4zh2ovB9rb66UF1sip49pNoWTS77uTh06-gzJ09RylpQlE

  3. The invited user will show in a new panel titled “Mailed Invitations”. To re-send an invitation, click the X button and re-submit the email address in the “Send Invitation” panel.

    https://lh6.googleusercontent.com/cYp-OmMOf_CvnDi0zRYS-qvB7rB9zkB5lmhfmdWhJjo--kOX6UfDWxJeDYzS_DBm55XQXnaM_lTtgJtvbd0MCaUHNFZadDtNzybsEgB4q0qNvUqZ86_YhzIUHk0M_kYOrvvagHzg