Medium system doesn’t allow to use ‘iframe code’ currently.
So you need to use GIF file to show your 360 image on Medium at this point.
Creating a GIF file.
From a smartphone
Export the 360 image data from your smartphone.
Then you can get the data as jpg, gif, mp4.
How to export data :
From a DSLR camera
You can create the GIF file with the image data sources created with Foldio360.
How to create the GIF file :