How do I avoid spending my Rubies by accident?

You have to leave a rubies purchase confirmation (at the beginning of the game this option is enabled by default). If you changed this option earlier and now you want to return it, do the following:

1.  Open the game Settings in the top right corner of the screen.

2.  Tap Notifications button.

3.  Tick Confirm using of Rubies in the Confirmation Settings window.

From now on a confirmation window will pop up every time you want to purchase something with Rubies.