There was a very similar problem posted a while back. They were also using a USB device, Audacity 2.3.0 and Mojave. (You have not said, but I assume that you are using Audacity 2.3.0 - if not, you can update from: https://www.audacityteam.org/download/mac/)
I bought a new MacBook Pro having Mojave and have the same issue with my pioneer DJMS9. Since there is no option to use the 3.5mm jack on MacBook to record with audacity I tried to use the DJMS9 directly for recording. Plugged with USB C, the MacBook recognizes the mixer and I can select my pioneer in the input window instead of the MacBook internal microphone. But I keep having the same issues: the sound preference window is saying „the selected device has no input control“ and audacity is giving the same error message „9997 Invalide sample rate“.
Any help is highly appreciated since I need to record a lot of music throughout my mixer to audacity.