You must be in editing mode to add background music to a publication page.
Click the Sound ♫ icon on the left toolbar.
Click Upload.
✅ If you have a previously uploaded sound file, it is saved in your Library — select it from there instead.
Select the required file from your device. Once uploaded, place it on the page.
Check the Autoplay checkbox in the right-hand toolbar if you want the sound to start automatically when the reader opens the page.
Save the page.