The error message "No Internet connection" in connection with Tune In also appears when the Internet access works, but the service itself is not available.
As a rule, these are usually short-term outages, for example, due to maintenance work. Be patient here, test the access again in a few minutes.
Alternatively, please disconnect your Raumfeld devices/host as well as your router and any access points used elsewhere from the power supply for 1 minute. After restarting the devices, you will in most cases have proper access to Internet radio via the Teufel Raumfeld app again.