You try to find time using FreeBusy on your google calendar and you get an error that reads, "Pardon the interruption, Find a time with FreeBusy has trouble loading".
This error typically comes up if your browser is set to block 3rd party cookies. When you use FreeBusy inside of Gmail and Google Calendar the browser considers freebusy.io a 3rd party website (because you are on calendar.google.com) and applies the policy to block 3rd party cookies.
If you are using Chrome, you can whitelist freebusy.io to exclude it from that policy:
Check if in chrome://settings/cookies you set "Block third-party cookies"
Add exception that 3rd party cookies be usable in
mail.google.comandcalendar.google.comin order for FreeBusy integration with Gmail and Google Calendar to work.
That's it, it should work as expected now!