How do I up my show rate?

For the past few months I’ve been running ads for my online service based business. I get about 2 meetings booked every day. I send out an appointment confirmation text and email when the person books a meeting, and then I send out a reminder text 30 minutes before the meeting starts. My show rate was 25% doing this.

Then I started putting “reply YES to confirm the meeting” at the bottom of the appointment confirmation text and that upped the show rate to around 35%. But that’s still too low.

What are ways (short of manually calling every person when they book an appointment ) that I can up my show rate?