When someone adds you to their SalesCal account, you get an email with an invitation link.
Open the link and follow the prompts. If you don't already have a SalesCal account, you'll create one as part of accepting. If you do, sign in and the team is added to your existing account.
Use the same email address the invitation was sent to. Accepting with a different address doesn't match you to the invitation.
You land in the account with whatever role you were given. Depending on that role and whether you take calls, you may be walked through a short setup covering your timezone, calendar, and availability.
You won't see every setup step. Some are limited to account owners, and steps like connecting a calendar only apply if you take bookings.
Being on a team doesn't automatically mean you can be booked. That requires a sales seat, which the account owner grants by turning on booking access for you.
If you're expecting bookings and none arrive, or you can't be added as a host on an event, ask the owner to check your booking access. They may also need to free up or add a seat.
Invitations expire. If yours has, ask whoever invited you to send a new one; it takes them a few seconds.
Other causes:
The link was truncated by an email client wrapping the URL. Copy the whole thing into your browser.
The invitation was cancelled or already used.
You're signed in as a different user. Sign out, then open the link again.
Check spam and junk first, then confirm with the person who invited you which address they used. They can see pending invites on their Team page and resend or correct the address.
You can be a member of several SalesCal accounts under one login. There's a team switcher in the dashboard for moving between them.
If one team's subscription lapses you'll be blocked from that team only. Your other teams are unaffected, and the block screen offers to switch you to one of them.
Ask the account owner to remove you. This frees whatever seat you held.