Music on Holds
Music on hold (MOH) allows to select which file to use for MOH. Only wav and sln file formats are available for MOH. You can have several files identified for MOH, among the media files loaded in your tenant or also in the Admin/General Settings/Media Files.
When using one or multiple files for MOH, you'll notice the file are not played from the beginning. This is made to save on resources, having only one process continuously playing MOH for all callers in the queues, listening to the same file. This configuration cannot be changed from the web interface, but only from the filesystem, by editing the file /etc/asterisk/musiconhold.conf and changing to "no" in the following section and then reloading moh module with "asterisk -rx 'moh reload'"
[general]
cachertclasses=yes ; use 1 instance of moh class for all users who are using it,
; decrease consumable cpu cycles and memory
; disabled by default
You can also use a streaming server to provide MOH, but beware, free services usually don't like the constant 24h/day bandwidth usage, so they change often their link or block abusers.
Just as a proof of concept, you can connect to https://www.internet-radio.com/stations/ pick up your preferred station and download the .m3u file. Open the .m3u file with a text editor and use that link in Music On Hold page.