Can you share an audio file from within your app to Soundcloud, using the Soundcloud app? That is :
It seems to me that Soundcloud does not support this, but I might be mistaken.
Note : Soundcloud used to support an iOS SDK. On top of that you would have to register your app at the developer portal of Soundcloud to get a unique key linked to your app.
The iOS SDK is no longer being supported by Soundcloud, and at this moment the Soundcloud website does “temporarily” not support registering any new apps, but it seems to be in this state for a long time.
No, this functionality does not exist in the SoundCloud app as a share extension. SoundCloud's old iOS SDK, CocoaSoundCloudAPI, did support this functionality. You can look at the code here to see how it worked (you'll have to find a CLIENT_ID to use since SoundCloud is no longer accepting API app registrations), or use the HTTP REST API.