Help Spotify not on music playlist

[markdoc]

I have multiple music apps on my HTC 10. When I tap on a song (mp3,m4a) my music apps come up on a list to choose which one I want to use. (Amazon music, Google, etc) Spotify is the only one not on the list. Does anyone know why and/or which setting to change to get it on the pop-up list?
Thanks in advance,
markdoc