It's possible you've already denied permission for the origin server you're using. Incognito has its own lists of allows and denials, separate from the usual Chromium mode you use.

To diagnose this kind of thing look at the console in your browser devtools. It may say "DOMException: permission denied."

Also, you can click on the lock icon just to the left of the URL while the page is displaying. It will show you the current permission situation, and give you a way to change it.