You can equip your bot with an Audio plugin, which embeds audio files of certain formats and size right in Messenger. All you need is a URL link to the file, which you paste into the plugin.
Important note: If the Facebook page connected to your bot (or its admins) are based in a European Economic Area (EEA) country, the audio plugin will not work. Even if not, audio your bot sends won't appear for EEA-based users. Get more information on Facebook's updated policies for Europe.
Supported formats: MP3, WAV, OGG
Maximum file size: 25MB*
*The maximum file size can be less than 25MB due to Facebook first transcoding the file before checking for its size. If the audio you provide is close to 25MB and does not render in Messenger, please try again with a smaller file.
Hosting on Dropbox
There is no reason to worry if you don’t have a hosting of your own — you can use any other hosting site, such as Dropbox, for instance.
If you’re going to use Dropbox, you’ll have to change the “www” at the beginning of the file URL to “dl”, for example: https://dl.dropbox.com/s/sample.mp3