For the longest time now Amazon has provided authors and publishers who distributed their audiobooks though ACX with promo codes that could be given to reviewers, shared with friends, and otherwise used to promote an audiobook.
It had been SOP for Amazon to pay a royalty when a promo code was redeemed, but that policy ended today. Kirsten Oliphant Posted this in her FB group earlier today:
To summarize, Amazon will still give you the promo codes, but they will no longer be paying when the codes are redeemed. Which, TBH, is only fair; I can't think of a good argument in favor of paying creators to promote their own works.