Cannot play personally recorded music on Echo/Alexa via Spotify

[Dacier1]

Spotify Premium on Windows 7 Desktop playing music on Echo/Alexa.  The new Echo appears to work fine with one exception - I cannot play personally recorded mp3 files (7 songs) on the Echo. I have played this music for more than a year on iTunes on the PC, on iPod, and on digital Walkman.  These files are not protected when I inspect file properties.  I created a playlist on Spotify with these 7 songs transferred from iTunes, but Alexa fails to recognize the playlist.  (I can play these songs via Spotify on the PC.)  So I added an 8th song from iTunes, originally from a purchased CD. Alexa now recognizes the playlist, but only the 8th song.  One obvious difference is Spotify's playlist window - the 8th song has a check mark to the left of Title while my songs do not.  Can anyone offer advice.  Thank you.