Cheers @Dotorimook, this post has really saved me. Just for anyone else, I needed to do similar and amend info.plist with hard coded values to make this work:
<key>IonApi</key>
<string>$UPDATE_API</string>
<key>IonMaxVersions</key>
<string>$MAX_STORE</string>
<key>IonMinBackgroundDuration</key>
<string>$MIN_BACKGROUND_DURATION</string>
To hard coded values:
<key>IonApi</key>
<string>https://api.ionicjs.com</string>
<key>IonMaxVersions</key>
<string>2</string>
<key>IonMinBackgroundDuration</key>
<string>30</string>