Just in case a supporter you invited missed the SMS invite, you can re-send the invite through the App.
To do this,
Tap on Settings
Tap on the Invitations button at the bottom of the screen. All pending invites will be listed here.
Tap on the name of the person you wish to re-send the invitation to
A prompt will appear asking "Re-send invitation"? Tap on Re-send.
If the mobile number was entered correctly, they should be able to get the SMS invite in a short while.
If the person is outside Australia, please make sure to add the country code. eg. +64 for New Zealand.