Martin sets a fee instead of a price
He picks Stripe, enters $50.00 and sets the payment option to Charge no-show fee. He also charges cancellations made in the last 24 hours.
Clara leaves a card, not money
After she picks Thursday at 10:00am, she types her card, ticks that she'll pay $50.00 if she misses the call, and presses Submit card.
The booking says Card held
The session sits in Martin's Upcoming like any other. The badge tells him a card is on file and nothing has been charged.
Thursday at 10:00, nobody joins
Martin opens the booking's menu in Past and picks Mark as no-show. Clara's name gets the no-show mark, and the fee is still uncharged.
Martin charges the card she left
Collect no-show fee asks him to confirm the $50.00. Stripe charges Clara's card, and she gets an email saying what the fee was for.

