First of all, please make sure you're using the latest version of Fade In for Mac (using Help > Check for Updates or, if you're using the Mac App Store version, by check for updates there).
In order to use dication, it may be necessary to enable advanced commands under System Preferences > Accessibility > Dictation > Dictation Commands by making sure Enable advanced commands is checked.
Please note that as of macOS 10.15 (Catalina), Apple has removed the functionality from Dictation that Fade In and other software has been using. We are currently looking at additional means to continue supporting voice input in Fade In. (See: "Dictation changes in Catalina – for the worse?")