Thanks for posting and reaching out to us today! Sorry to hear that you aren't getting any audio to one of your sleepbuds, I would love to look into this further for you.
Let's start with ensuring that your Sleepbuds are running the latest software via connecting the Sleepbuds to a PC and visiting the Bose Online Updater, then following the on-screen instructions. We can also perform a product reset on the Sleepbuds, this can be performed by inserting a thin paper clip or pin into the hole on the back of the case near the USB connector. Press until you feel a click.
Please can you also try some other sounds on the Bose Sleep App as well as testing them with another device?
I look forward to hearing back from you with the result of these steps and if any other users are having this issue please do let us know.