Make sure you Rødecaster pro is connected, turned on and Visible on MacOSX. Select on OSX output Rødecaster stereo output and for input select the Rødecaster Multitrack device.
Check if your Rødecaster pro is getting input from your microfoon (or other devices), by checking the volume bars on the device.
In OBS check your audio device setttings, It should be the RodeCaster Pro Multichannel.
In the mixer, my microphone show up as, MIC/AUX3, and make sure this device is enabled in the Scene.
Now you should be able to record audio through the Rødecaster pro within OBS.