It's on both calendars. That's handled. Right?
Not quite.
People don't ghost because they stopped caring. They go quiet because by Thursday they feel bad... and feeling bad makes people hide.
It's easier to say nothing than to send a message admitting you forgot.
So your reminder isn't just a reminder. If it's not written right, it's an exit - a way out that doesn't feel awkward.
The move: send three reminders. When they book, the day before, and the morning of. And every single one of them ends with the same line: 'If that no longer works, just let me know.'
Now the people who can't make it tell you Wednesday. And you fill the slot.