Booking flows work very similar to purchases:
Select a class or appointment
Sign in or sign up
Confirm the booking and credits will be deducted
To confirm the booking the user needs to have enough credits to complete the booking (even if joining the waitlist). In the event they don't they can quickly purchase a package without leaving the booking flow.
It's essential that you always have packages available for purchase online for all classes and appointments that you offer.
How The Quick Purchase Flow Works
Before confirming the booking they can click to purchase credits.
They can choose from suitable available packages.
Pay for it at checkout.
They will be returned to confirm the booking.