Check out the latest version of the game: It brings a new feature to gather ruby for free by watching rewarded ad videos. Open the promotions screen (for example by tapping the ruby display on the main screen) to start this option. We are introducing this explicitely as a test run, so your feedback is important for us. Note that currently you get 2 ruby for watching an ad video, and the usage is limited to 10 times per hour.
Furthermore, this version drops support for the MQTT mode for technical reasons. You don’t need to change anything, and the game will continue to work as before for you.