Sparpreis Aktion is a nonflexible, nonrefundable fare which is only valid on long distance trains. As soon as you would choose a train connection which include a local train, you are only offered the regular Sparpreis (which starts at 29 Euro, compared to the Aktion one which starts at 19 Euro). This also means, that if you choose the Sparpreis Aktion to Köln Messe/Deutz, you would have to purchase a second ticket, if you want to connect with local trains or S-Bahn from there to another station in Cologne.