Do you mean this one?
https://boost.com.au/shop/150-prepaid/
That is only for new sim pack purchases (for new customer joinging Boost). It does not apply to existing customer recharging.
There was recently a Boost recharge voucher sale on through Coles instore, though. That finished a couple days ago.
* I am a Boost Australia customer. This is a peer to peer community where users help each other.