Why are my Apple Music purchased songs no longer available on my iPhone?

When I attempt to play songs on my iPhone that I purchased years ago I get a pop up stating, "This song is not currently available in your country or region." However, it is playable via iTunes on my PC. I'm not sure why it is available on one device but not another. Any suggestions or ideas on what the issue may be would be greatly appreciated.

Thank you :)

[Re-Titled by Moderator]