When people click on the link on their phone, it opens the Soundcloud app but doesn't take them to the audio file.
Best answer by Echo Drone
On desktop, you can click on the share icon under your private track, and copy the private link given to you there.
On iOS or Android, you'll only be able to private share via the SoundCloud Pulse app. Unfortunately, it is not possible to private share through the SoundCloud app specifically. All you have to do is log into your SoundCloud account through Pulse, go to your private track, then share & copy the link. It will then copy your private link.
Let me know if this helps!