A card is required to start, but you won't be charged until the trial ends. The first 20 workspaces to pay their first invoice lock in the founding-member rate for as long as they stay subscribed.
Next you'll add a card on Stripe's checkout page. We won't charge it for 30 days. When the trial ends, the plan you picked starts on its own and renews until you cancel. You can switch plans or cancel from Settings → Billing before then, and if you cancel during the trial you pay nothing. By continuing, you agree to the Terms of Service.