On the form you submit to request permissions, they have an option they deem valid: "My app allows people to login with Instagram and share their own content. ". You then go on the explain what your app does. However, I don't see how this is possible, since the only endpoints available are all GETs, you can't post (share) anything. Am I missing something here?
You misunderstood share word meaning in this context. Sharing does not mean posting. It means that you help the users to share their own content by the features of your app, such as creating widget that they can embed (share) on their own website.