Online schedule system on Safari

I am trying to use an online schedule system called "schedulepoint" and I have been unable to make an appointment using this system with Safari. I can view all schedules and do everything else but not actually make an appointment.

After selecting a date and time for a lesson, and doing everything as I normally would on a PC I click the button marked "schedule" and the following error message pops up

"https: www.schedulepoint.com"
"Please make appropriote changes, you can't create a schedule in the past"

I have tried messing with all the settings and prefernces on Safari and my computer but to no avail.

I just can't seem to figure out why it will not let me make an appointment using this online system.

Can anyone help me with this issue? Or at least give me an idea on what to troubleshoot.