Background: I'm learning Apple Wallet by creating a barebones sample app and am trying to automatically update a pass. In order to do so, I understand I need to run a web server that sends push notifications to the device when it's time for the pass to update. I'm using Apple's sample code and running their Ruby webserver via localhost. It correctly generates a .pkpass file, which I can add to Apple Wallet in the simulator by visiting the localhost site or by dragging in the .pkpass file.
Problem: This process doesn't work on my physical iPhone. When I go to the localhost on my iPhone, it shows a 200 response code but comes with the popup "Safari cannot download this file." Even if I try just emailing the generated .pkpass file to myself, it won't open in Wallet.
For anyone who may be wondering, I got it to work by changing the web host to https. Then I ran into another problem getting automatic updates to work, solved here: How to allow HTTP webServiceURL in apple wallet's pass.json file