You will need a mp3/m4a file, stored in a DropBox folder.

Locate this file, right click and select "copy DropBox link". This will place the URL for the selected file in your clipboard.  Example:
https://www.dropbox.com/s/gw71hmcxyc9d8e0/A%20Closer%20The%20Poster%20%281%29.m4a?dl=0

Using the supplied URL will result in DropBox's presumption that you want to download the cloud-stored file.  In many cases this is correct.  For this purpose, however, it is not - we want to stream the file contents (and audio file) to listen to it live.

To do this we need to edit the supplied URL, removing the last few characters "?dl=0" replacing it with the character "?raw=1".  Example:
https://www.dropbox.com/s/gw71hmcxyc9d8e0/A%20Closer%20The%20Poster%20%281%29.m4a?raw=1

This revised URL can then be used in any of the message fields in BlindSquare.  You can expect a short delay while the connection to DropBox is completed.

The example above is associated with a QR  used to amplify the message provided visually on a conference poster.  This, provides not-only added information for sighted readers but makes the information on the poster fully accessible when the printed BlindSquare QR is read.