I ran into this strange problem today where HTTP requests stopped working on iOS alone. Even though I have the latest Ionic CLI, my project was running Ionic 1 still.

To solve this http error I removed this plugin:

ionic cordova plugin remove cordova-plugin-ionic-webview

And added this to config.xml:

<access origin="*" />
<allow-intent href="http://*/*" />
<allow-intent href="https://*/*" />
<allow-intent href="tel:*" />
<allow-intent href="sms:*" />
<allow-intent href="mailto:*" />
<allow-intent href="geo:*" />

Probably a bit unsafe to allow everything but had to get it working again.
If this doesn’t work for you try to also remove the iOS platform and re-add it.

good luck~