Unable to access Android SDK add-on list

There could be several reasons why you are unable to access the Android SDK add-on list. Here are a few things you can try:

1. Check your internet connection: Ensure that you have a stable internet connection as the add-on list requires an internet connection to be accessed.

2. Check your SDK Manager settings: Make sure that your SDK Manager settings are configured correctly. Go to the "Settings" tab in the SDK Manager and check that the "Force https://... sources to be fetched using http://..." option is unchecked.

3. Clear the cache: Clear the cache of your Android SDK Manager and restart it. This can help resolve any issues with accessing the add-on list.

4. Update the SDK Manager: Ensure that you are running the latest version of the Android SDK Manager. You can check for updates by going to the "SDK Manager" tab and clicking on the "Check for Updates" button.

If none of these solutions work, you can try reinstalling the Android SDK or seeking help from the Android Studio community forums.