Most "plusbus" tickets are sold as separate tickets rather than one inclusive train and bus ticket. For example someone the other day wanted a ticket from Huddersfield to Manchester to include the bus. I entered "Huddersfield" to "Manchester+bus" and the Avantix returned "No Fares Found". I had to sell two separate tickets - "Huddersfield" to "Manchester STNS" and "Manchester STNS" to "Manchester+Bus".
As a result, provided you have any type of train ticket, you should just ask for a ticket from "Paignton" to "Paignton+Bus".