From time to time American Express run promotions for existing card members who add a supplementary cardholder to their account.
It's free to add additional cardholders to your account (no credit checks required) and while it's an excellent way to maximise Amex offers (you can save those to multiple cards) and points earn, keep in mind you are responsible for any charges to that card.
Right now, when you log in to your account, you will see a pop-up and also a permanent banner message at the top with the following promotion:
Receive 5,000 Bonus Points when you add an Additional Card to your Account & they spend $500 on their new Card by 31 July 2019. Limited to 1 Additional Card. T&Cs Apply.
This time around the promo is only for 1 supplementary card per account whereas in the past it was possible to add 1 sup for each different Amex card product you might have.
How to maximise this offer?
Since Amex Membership Rewards are only worth half of what they used to be, your best option is to apply for a sup card under a co-branded card such as Qantas Ultimate or Velocity platinum. Both cards transfer at a 1:1 rate so you will get the full 5,000 points.
It's very possible that those with Westpac cobranded Amex cards are excluded from this promotion, but it's still worth checking! When I called up, the phone team wasn't aware of the promo, so it appears to be available online only.
Don't have an Amex yet? Check out the latest bonus points offers here.