1/ Go to the current bookings screen (magnifying glass)
2/ Go to the administration part of the booking
3/ Add a payment to the booking
4/ Fill in the amount and check the credit card
4/ Check if the charge was succesful
If the charge was succesful you will get a green sign and a success message (scrolling over the icon)
If the charge has failed you will get a red sign and a fail message
You can check the Stripe dashboard to find out why the payment didn't succeed.