I purchased an advance bus ticket from Coimbra, Portugal to Salamanca, Spain (saving 20 euros a tkt) and the system reminds me of Renfe (nightmare). In case anyone else is trying I got it to work by using the Spanish website and paypal. No english, no credit cards.
Salamanca is AMAZING!!! Message me if you have any questions, I lived there for 6 months last year!!
This looks pretty straight forward:
http://www.movelia.es/en/