You can use these ways to share an unpublished Squarespace site.
Option 1: Set your site to password-protected and send the password to the person you want to share.
#1. First, choose Settings
#2. Next, choose Site Availability
#3. Choose Password Protected then enter your password
#4. Save.
#5. When users access site, just enter password, they can access the site.
Option 2: Change the site to private then add Contributor or Viewer permissions
#1. You can follow this guide to add a Contributor.
#2. Choose Viewer Permissions
