Your plan includes a fixed number of sales seats plus one workspace seat. Understanding the difference explains most "you've run out of seats" messages.
A sales seat belongs to anyone who takes calls. If a person can be booked, they hold a sales seat.
Solo includes 1 sales seat
Pro includes 5 sales seats
If you take calls yourself, you occupy one of these seats. On Solo that means the single sales seat is normally yours.
A workspace seat belongs to someone who needs access to the dashboard but never hosts bookings. An operations manager, a VA managing your calendar, or a marketer checking lead data.
Both plans include 1 workspace seat on top of your sales seats. It doesn't cost extra and it can't be used to host bookings.
On Solo, with you taking the calls:
You hold the 1 sales seat
You can invite 1 more person as admin-only
On Pro, with a team of five taking calls:
You and four colleagues hold the 5 sales seats
You can invite 1 more person as admin-only
Booking access is what turns a workspace member into a sales seat holder. Go to the Team page and turn on booking access for that member. If every sales seat is already taken, you'll need to free one up or add another seat first.
If you try to add someone as a host on an event before giving them booking access, you'll see:
This member doesn't hold a sales seat, so they can't host bookings. Give them booking access on the Team page first.
"All sales seats are in use." Every seat on your plan is taken. Either remove booking access from someone who no longer takes calls, or add a seat.
"Your Solo plan includes 1 workspace seat, and it's in use." You've invited your one admin-only member already. Moving up to Pro raises this to 5 sales seats.
"Round Robin routing is a Pro feature." Multi-host events need Pro. Solo events can have one host.
Removing booking access from a team member releases their sales seat immediately. They keep dashboard access as a workspace member. Removing the person from the team entirely also releases the seat.
Pending invitations count against your seats too. If you've invited someone who hasn't accepted yet, that seat is reserved until the invitation expires or you cancel it.