Hi all Grav webmasters and developers!
The Grav version is 1.7. Web browser is Mozilla Firefox 89.0 (x64) under Linux Mint.
When I tried to upload MP3 file to my blog page in Admin mode,
I got error "The mime type does not match to file extension"
The solution of the problem is to edit file /system/config/media.yaml:
And then upload file MP3 again.
Bottom line: the right MIME type for *.MP3 files should be audio/mpeg, not audio/mp3.