This is likely because you have not granted access for specific apps on your device.
Apple
In iOS, under Settings > Privacy > Microphone (or camera), there are app-level settings for access.
If you have turned off access for an app (in the example below Chrome has no access to Microphone), then Vowel cannot ask for Microphone permissions. You must first go to Settings > Privacy > Microphone, and enable access to whatever browser you are using, then return to the browser and attempt to access the Vowel meeting again.
Make sure you do this for both Microphone and Camera.
Android
Open the Settings app on your phone and go to Apps and notifications. Scroll down to locate Chrome on the app list.
Next, go to Permissions. Here, you’ll find a list of permissions for Chrome.
Tap on the Camera option and select Allow only while using the app.
Now go back to the App Permissions page. Tap on Microphone and select Allow only while using the app.
After allowing the required permissions to the Chrome app, you’ll need to explore Site settings in Chrome to make sure that the websites are allowed access to Camera and Microphone. Read on to learn how.
Launch Google Chrome on your phone. Use the three-dot menu icon in the top right corner to open Settings.
Scroll down to the Advanced section and tap on Site settings.
Go to the Camera option and toggle on the switch to allow websites to use it.
Now go back to the Site settings page, tap on Microphone, and toggle on the switch to enable it.
Make sure you do this for both Microphone and Camera.