I have Appointments+ and MarketPress integrated - there are a few problems, but recently - last couple of days the Coupons has stopped working on the checkout.
Literally nothing happens when Apply is clicked.
To Reproduce ( You'll need to signup )
Add a rehearsal - http://www.silverstreetstudios.co.uk/my/store/products/rehearsal/
At Cart you can try BOSSMAN100 - it's a 100% discount.