You can start using Apple Pay as soon as you add your Greenlight card to your Wallet. Remember to add your cards to any device that you want to use with Apple Pay.
Greenlight and AppleCare are ready to help you with issues when adding your Greenlight card to your device. You can contact us or AppleCare, which will help you resolve your issue.
Get help adding your Greenlight card here: https://support.apple.com/en-us/HT205630
Integration with Android Pay is coming soon!