Local files (owned MP3s) not playable?

[MannStooka]

Plan: Premium

Country: USA

Device: Samsung Note 8, PC

Operating System: Android Oreo, Windows 10

My Question or Issue:

Checking out Spotify as I transition off the dying Microsoft Groove platform. My biggest concern at the moment is I have a lot of music that has been converted to MP3s over the years from physical media that I own - there are numerous songs that are not available for play within Spotify and I don't understand why this is happening. These are all setup in my local file directories within the app, why are these unplayabe?

[MannStooka]

Bump.