ROFL, I can just imagine a journey with a kilometer long cable to the internet box.
I searched for it on my trusted search engine and apparently there are occasional problems with DRM on the FireTV Stick.
I assume you don’t have another streaming stick or an HDMI cable from the tablet to the screen at hand? (You may be able to buy the cable in the Swisscom shop and exchange it after 14 days if it does not work as desired).
P.S. If you have TV M or higher: Does the same message appear when playing bluePlay content?