As far as I know I cannot download a VPN on to a Chromecast dongle. It just mirrors what I am using to cast (laptop/phone) . I just have to sign in to the wifi with the Chromecast and the laptop does the rest. Done it MANY times. This internet service would not allow it. I normally can cast to the device with or without the VPN which was only used to access NFL Sunday Ticket on the laptop...not the Chromecast which, again, just mirrors what I have in front of me....and definitely not ever initiated by the Chromecast which only requires me to sign in to the wifi

Edit: Soooo after some research the VPN has to be uploaded onto the physical or virtual wifi router (not the Chromecast) so that both the Wifi router and the laptop/phone are on the same network. WAAAAY too complicated an install for a football game