Thank you for looking at this issue for me.
The following is in the log file. The test sound file “Meeting_switch_unset” is loaded on to the system, I use it elsewhere in my pbx quite successfully.
2503[2021-07-11 12:33:34] WARNING file.c: File custom/Meeting_switch_unset does not exist in any format
2504[2021-07-11 12:33:34] WARNING file.c: Unable to open custom/Meeting_switch_unset (format (slin)): No such file or directory
2505[2021-07-11 12:33:34] WARNING parking/parking_applications.c: ast_streamfile of custom/Meeting_switch_unset failed on Local/820@ext-paging-000001c8;1
I then did a little more digging and found the custom sound files in /var/lib/astrerisk/sounds/en_Au/custom
Note the en_AU which is my chosen system language. The module Park and Announce is successfully using customs sounds in other parts of the app so I assume this is an issue with that segment of the app?
As a work around I guess that I can make a copy of the required sound files in the “en” directory but you may be able to indicate an error on my part.