Note that this feature is only available in the Advanced plan.
When chatting to a fan you will notice a new icon below the message field:
By clicking on it the audio panel will open:
You have two ways of uploading audio files:
1. Clicking on "Choose file" and selecting the file manually.
2. Just dragging your audio file and dropping it in the "Drag & drop your files here" box.
An other popup will open where you can specify a name and a description for the audio:
After clicking Upload audio the audio will appear in your panel, now you can select it...
and click "Add audio" to add it to your message: