@elisedoppel
I'm going to flag this post for the Zapier Community Team. They should have more insight on this and can escalate to the support team if needed.
Sit tight, and someone will contact you soon.
Hmm, I’ve not come across this one before but I did some digging and found something that might relate to this.
If the post on your timeline is a post that was shared from another page or person, you will not be able to share the image from this post somewhere else, such as Twitter, another Facebook page, etc. This sounds a lot like what you’re describing: the image in the post is from Instagram and so other users can’t share the post to their pages.
If that’s the case, then you could try adding a step in your Zap where you upload the photo from instagram into a file sharing service, like Google Drive or Dropbox and then use the file there to create the post. If that doesn’t sound like a good fit for you then it might be tricky to make this work. If you are having trouble with the workaround then I’d recommend reaching out to the Zapier Support Team using the Get Help form and be sure to mention what you’ve tried so far.