On the free plan, when you hit the 10 reminder limit, it says:

Free accounts only allow you to set 10 reminders at a time. Consider upgrading your account (plans start at only $24/month) and you’ll be able to set up to Infinity reminders. Learn more about the benefits of upgrading your account.

But plans actually start at $7.

Maybe that’s because full-featured plans (including the message board) start at $24.