How to play internet radio stations in the Music app on iOS 13?
Solution 1:
My guess is that it has something to do with your location. I'm in the USA and when I searched for "hr3" in the Music app it immediately showed that station you are looking for as a result. Maybe TuneIn only works with the Apple Music app in some countries?
Solution 2:
I don't know if it's still possible, but at the time, I was retrieving the streaming URL, I going to iTunes > file menu and opening a link (or something of that style). Once the link played on iTunes, I had a playlist named radio, I added it to the playlist and synchronized the playlist with the iPhone. If iTunes could read the streaming format the iPhone too. I don't remember the formats he didn't support, but there are very few for me. To be sure that your url contains only the streaming URL you test it on a browser, because I already had url that looked like the stream, but it was not the case. If you just have a player it's good, it's the stream URL. If you have a web page, you must continue your research. I would get the url in the source code of the pages ...
Solution 3:
Tell Siri to play it. E.G. there is a radio station here called 101.1 ESPN. I tell Siri to play 101.1 espn and it usually works minus content restriction bs.