Square Appointments -- Automatic Service Charge or Gratuity

[samkw]

We will be using Square Appointments for our day spa.  At checkout we need to apply an automatic 20% gratuity/service charge using Square Register.

Unlike Square for Restaurants, this doesn't appear to be an option for Square Appointments -- is this correct?  If so, are there any effective workarounds to provide this function with the current product?  It appears this has been an outstanding feature request for multiple years.

Candidly, I may need to find a different POS solution for the day spa if I can't find a reasonable workaround for this function.  I also want this for online service sales as well, but for now I'm focusing on in-person Square Register checkouts.  Thank you for any useful suggestions that can be provided!