Can't download and play local files on mobile

[RadekH]

Plan

Premium

Country

Czech Republic

Device

Xiaomi Pocophone F1

Operating System

Android 10 / Windows 10

My Question or Issue

So I've been trying to play my local files on my mobile, but for some reason I can't download/play them. I've uploded the files from PC and put them into playlist. The PC can play them without a single issue, but when I try to download or play them on mobile it shows, that there is a problem (I guess, there's just this grey exclamation mark). There's no problem with downloading "official songs" from Spotify, even if they are in the same playlist. I have tried everything:

• Both devices are connected on the same Wi-Fi (even tried hotspot)
• Both devices should be synced (since I can control music from one on another)
• I tried reinstaling and relogging on both devices
• Moving the files in PC to different places
  
• I tried different files (even created a new one)

I tried everything I found in other threads (please don't send me link to this, I'm sick of that page). I've no idea of what to do. Please help.