...cose problem looks is easy to solve, but i didn't find this at forum.
It sounds easy, but if it's what I think it is, then this is actually one of the hardest MusicBee puzzles I've personally had to solve thus far.
A link to an identical problem from the past:
https://getmusicbee.com/forum/index.php?topic=37129.msg204206#msg204206What makes this kind of puzzle particularly hard to solve is that what the template editor shows is not what goes on behind the scenes.
Your formula is trying to match a backslash, and the template editor is indeed picking it up.
However, the actual sync settings are not because the backslash is an illegal filename character.
By default, it's replaced with a whitespace.
So internally, MusicBee only recognizes a whitespace, and not the backslash (contrary to what the template editor would lead you to believe).
A screenshot of your sync preview will show this, I think.
Anyway, just follow the instructions in that linked post to replace the backslash with a more unique character than a whitespace.