When Turning Down An Invitation messages in a Professional tone

I appreciate it, but I’m not free that day.

I’ll pass this time—hope it’s great.

Thanks for inviting me—I’ve got to sit this one out.

I’ll pass this one, but let’s do something soon.

I’m booked already, but let’s plan something soon.

I’ll pass for now, but let’s plan something soon.

I can’t make it, but let’s catch up soon.

I won’t be able to join, but hope you have fun.