Cannot set a purchased song as a ringtone

I’ve recently purchased a song from itunes, I attempted to set the song as a ringtone when receiving a call. When I go to:

settings>sounds and haptics>ringtone>

the purchased song does not show up in the selection list.

if I then go to:

Tone store>purchased>music>all songs> select “rebirthing”

there is no option to select the song further.

I’m disappointed because I purchased the song specifically for ringtone use.