This is a posting from someone who submitted a test.
https://forum.audacityteam.org/t/how-to-send-a-test-to-acx/49588/1
These are the ACX instructions how to submit a book. This will also give you a link to all the other ACX resources from the listings on the left.
https://www.acx.com/help/acx-audio-submission-requirements/201456300
We would add saving your original WAV recordings against computer failure, and create WAVs of the Mastered Work in addition to the ACX submitted MP3. That’s your archive. You can’t easily change or edit the MP3 without sound damage.
Be able to point to two separate places that have valuable work. Your computer and a separate drive counts as does cloud storage or thumb drives. Two different places on your computer does not count.
Koz