I was invited to a seating chart. How do I accept?

Open the link in the invitation email. Sign in, or sign up if you are new, type the invitation password if one was set, and the chart opens. From then on it is listed under Your events at planseats.com/app/shared.

Sign up with the email address the invitation was sent to. An invitation opened while signed in to a different account still asks you to accept, and it goes to the account you are signed in with.