How can I see how much of my plan's limits I have used?

Open Configurations, then Plans under the Plans and billing section (owners and admins). Click "Over-usage billing" at the top of the page to see this month's tickets and chatbot sessions: a bar shows how many you have used of the included allowance, how many additional ones you have approved, the price per additional ticket or session, and any accrued over-usage cost. For the fixed limits (mailboxes, forms, automation rules and so on) the owner's plan comparison table shows your usage next to each limit in your current plan's column, and hovering over the number displays "Used X out of Y".