https://forum.audacityteam.org/t/audiobook-mastering-version-4/45908/1
This is a long-winded way of introducing a three-tool process. It is a “suite,” a harmonious grouping. The tools create intentional errors and clean up after each other. Don’t ad-lib.
If you have a quiet, well-behaved recording, it’s possible to go from Mastering 4 directly to making the MP3 for ACX.
If it still fails, you can announce a test sample and post it on the forum.
http://www.kozco.com/tech/audacity/TestClip/Record_A_Clip.html
Home recording artists rarely pass noise the first couple of tries. It’s hard to describe how quiet -60dB is. In English, they want your background noise to be a thousand times quieter than your voice.
And while I’m here, it’s good computer hygiene to make WAV (Microsoft) 16-bit protection sound files of your original readings and your Edit Masters. Audacity Projects are not recommended for this.
Koz