configuration of an external RSS calendar

Hi, I’m using Every calendar+1 version 2.1.1.
I understand from the website that a RSS calendar can be printed by this plugin.
However, I tried to add a RSS external calendar but I can not set “External Calendars” to a RSS value. I have 2 choices : “Google Calendar” or “CiviCRMProxy no URL required”.

I looked at the doc (https://docs.google.com/document/pub?id=1QwmBusfl0gfRVkIt_PomAI3reG3B8Ae45-xCt1Q0uFw) but pictures resolution are too bad to allow me to check the fields.

Could you confirm me that RSS external calendar are allowed to be printed by this plugin ?
Thanks,

https://www.ads-software.com/plugins/every-calendar-1/