I received this in multiple emails, seems to be a decent deal for returning customers.
I also believe this isn't targeted as I was able to activate this offer on my account that just had its subscription end today, despite the email being sent to my other account. Furthermore, I created a new account to check again and was also able to access the same offer using the link sent in the original email. However, please don't take my word for it.
This promotion is valid from 15 June 2022 to 11:59PM AEST 15 July 2022. The promotion is valid only for email recipients of the promotional email inviting recipients to participate in this promotion, who sign up for an Audible membership at www.audible.com.au by clicking the link above. With your membership, you’ll get one credit per month for $0.99 in your first month and $0.00/month in the second month. After the first 2 months, your membership will renew automatically at the regular monthly price, currently $16.45. Cancel anytime. The promotion applies only to items sold by audible.com.au when clicking the link above. The same items sold by other sellers (e.g. audible.com, or audible.co.uk) do not qualify. Claim codes cannot be resold, transferred for value, redeemed for cash or applied to any other Audible account, except where required by law. This promotion may not be combined with other offers. Limit one per customer and account. Audible account required. Other terms and conditions apply, including those available at https://www.audible.com.au/legal-terms/Conditions-of-Use?mod… and claim code terms and "conditions at https://help.audible.com.au/s/article/what-are-the-condition…. If you violate any of the terms or conditions, the promotion will be invalid, and the offer will not apply. Audible reserves the right to modify or cancel at any time. Any terms prohibited by law shall be void without prejudice to the remaining terms.
Worked for me and I only recently ended my sub about 2 months ago.