You cannot share media on Instagram using the API. See the docs:
At this time, uploading via the API is not possible. We made a
conscious choice not to add this for the following reasons:
- Instagram is about your life on the go – we hope to encourage photos
from within the app.- We want to fight spam & low quality photos. Once
we allow uploading from other sources, it’s harder to control what
comes into the Instagram ecosystem. All this being said, we’re working
on ways to ensure users have a consistent and high-quality experience
on our platform.