Note: Advice in this article will only work for DotNetBrowser 1.
See the corresponding article for DotNetBrowser 2 here.

Voice recognition is one of those Chromium features that uses Google API. You must enable Speech API and billing, otherwise voice recognition will not work.

Once you enable Speech API and billing, you can provide the keys to DotNetBrowser Chromium engine using one of the approaches described in the Chromium API Keys article.