Increaseing RMS in Garageband

I found an answer regarding increasing RMS in garageband in the community chat from 2 years ago that said your settings should be set at what I have inserted. Mine are aleady set exactly this way and yet ACX is saying that my RMS (dB RMS) is too low for my audiobook submission. My files are reading -24.8 dB and they are saying they need to be at least 1.8 dB. What do I need to do?