It says right above that box that it requires the WHOOGLE_CONFIG_PREFERENCES_KEY or that option will be ignored. My guess is that you have to manually edit some config file to turn that key on, or generate an encryption key yourself that you provide through editing a config and adding it to that line.

Edit: you probably need to add your own domain or IP as the root URL too.

My ex wife turned out to be a Lenovo. She and her new girlfriend seem very happy. /s