Sorry to have to tell unsigned artsit that is being promoted by +CreateSpace. CreateSpace will no longer distribute MP3s as of October 15, 2014. They are constantly evaluating there service catalog and have decided to discontinue support for MP3 as wthey work to provide customers with the most cost effective and valuable services.
Distribution will continue until October 15, when all MP3 titles will be removed from the Amazon Digital Music Store and CreateSpace. You will continue to have access to your account, title information and royalty reports. Payment for any remaining MP3 royalties, regardless of threshold, will be issued within the regular MP3 payment timeline.