To embed an interactive version of your prototype into an Avion user story, you need to generate a share link from Axure. You can do this by clicking Share — this can be found on the right at the top.
In the next window, make sure Publish to Axure Cloud is selected and click Publish.
Once the publish is complete, you will receive a notification. In this window, click Copy Link.
This link can be pasted into your user stories in Avion under the Attachments menu. Avion will recognise this as an Axure link and give you an interactive embed. This will stay up-to-date as you change your designs, as long as the link remains visible to Avion.
You can also restrict your shared prototype to only display certain pages by configuring your share link and unchecking Publish all pages. Then select the pages that you want to share.