First contact the radio station office, by phone or email an obtain a written “OK” from they.
Implementation:
For android is no problem.
For iOS : at the Apple review you have to explain why is this more than a simple URL open, via browser. So you should add some platform feaures to be accepted.
Contacting they is not only for law, but they (should) know about you and maybe they will update they site with 2 link: download from Google Play or AppStore ( those 2 links)
If they know it is 15000 device is listening they, maybe they will upgrade the hardware too, bandwidth too.
I hope it helps.
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solved Using streaming radio URLs is legal to develop commercial apps? [closed]