You can't use ACX download codes for advance review copies, because they only become available when the book is actually live. In addition, ACX has severely limited the number of review copies (25 US & 25 UK on release; then another 25 each once you've made the requisite number of sales). Spotify codes are limited to 100 unless you choose Voices Plus distribution (not recommended, see Distributing Wide.) Additionally, at this time Spotify only allows ratings, not written reviews.

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You can use Spotify codes for ALCs, but there is a waiting period. According to Findaway Voices customer service,

 

"Once the audiobook has passed our review, it may take 3 to 5 business days to be able to generate redemption codes from the redemption codes tab of your titles project page. If you are unable to generate codes 5 business days after the title passed our review, please let us know."

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You cannot get ALCs via Author's Republic. Promo codes are available via Audiobooks.com after the audiobook is live on that channel. The number does not seem to be limited.

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HCB uses Bookfunnel to distribute ALCs to our curated list of vetted reviewers.

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Reviews are collected prior to the audiobook's release (if you have set a release date) and then Audible or Spotify codes are shared only with the top reviewers, to be posted as close to the live date as possible.