After enableing the voice output in RyngDyng app the “choose voice” dropdown list is empty and not working. It seems voice output isn’t working.
The RyngDyng App is a “Web App” which means that is essentially made of web pages and running within a browser. Therefore, all resources such as voice output depend on what the used browser offers.
Please try to start the app using an alternative browser, maybe also on a different device (it can be any device with a modern browser). The speaker drop-down will show the voices the used browser offers.