This strategy outlines the simple ways I manage session timings and tracking parent payments using Google calendar. I think that the simple processes are the best and it saved me around £80 per year with dedicated software.
As your client base grows, you can automate this process to save you some time but for fewer than 10 students, this works really well. It also alleviates any queries because I can match up the dates with my Zoom logs to prove to parents the number of sessions they have had. Bonus!