Hi Javier Basilio,
We'd like to know more about the issue. It would be great if you can reply to these questions in order to assist you further.
- Have you already install the Cortana App on your Galaxy S8?
- Is there specific error message?
- No sound but the Galaxy S8 is playing audio?
- May we know the Android version?
- May we know the region/country you are located?
Cortana isn't available on Surface Headphones in all countries and regions. We can avoid issues on your Surface Headphones by keeping them up to date with the latest improvements.
- Set up your Surface Headphones in the Cortana app.
- Open the Cortana app, then select the Devices tab. Go to the Devices menu and choose Surface Headphones.
- If an update is available, tap Update Now. To check for updates anytime, select Surface Headphones > Updates > Check for updates.
If Updates wont fix the issue, since you already do the basic troubleshooting, we suggest contacting our Surface Support for further assistance with the issue on your Surface Headphone. Rest assured that our assisted support will be able to help you better with the advance troubleshooting steps needed to resolve the issue.
For additional information about the Surface Headphone's functionality, see this article.
Regards