Can anyone help me with this error?

The replace command in the image is not working.
Any clues why?

I think that _FILENAME does not include the extension - this can be found in _FILENAME_EXT.
So you simply replace .flac with nothing (leave out the .mp3 in the search term).

There are different methods available to reach the goal, here are some examples.

From: Test.flac.mp3
To: Test.mp3

Convert "Filename - Filename"
Old filename pattern: %1.flac
New filename pattern: %1

Convert "Tag - Filename"
Formatstring: $replace(%_filename%,'.flac',)

Convert "Tag - Filename"
Formatstring: $replace(%_filename%'.','.flac.',)

Action "Replace"
Original: .flac
Replace with:


Thanks, let me try this.

thank you both