I have a coupon where the customer needs to be logged in before they can use it. At the moment the error message is just "Coupon code xxxxxxxx is not valid."
Is it possible to change this and detect that the coupon requires the customer to be logged in and to report that in the error message
I reckon you should check this module that was developped during a Magento Hackaton:
https://github.com/magento-hackathon/Hackathon_PromoCodeMessages
It basically provides improved error messages when a promo code is submitted.
If this does not provide the error message you need, I reckon you can modify the Validator model to add an extra message. Feel free to make a PR if that's a global improvement to the module.
you can try this extension, i dont know this is completely done or not, it may work for you : https://github.com/magento-hackathon/Hackathon_PromoCodeMessages
