On android Playlist songs are not playable

For each song included ina playlist the message is always the same: this song cannot be played.
You must solve

Hi Save dev,

please make sure the songs are playable in the Google Play music application.

If that is the case, could you please send us one exemplary sound file via support@algoriddim.com?

Thank you in advance and our apologies for the inconvenience.

Lukas E.