These may well be two different problems and anyway would be good not to mix up different things. Nobody here knows your system and the devices you have or what you are doing, unless you tell us 
When was the last time the Mu-so worked? Did you recently update Roon, maybe for the first time in months, and did it stop working after that?
I am asking because at the end of June an update was released that enabled AirPlay 2 in Roon. Most older devices remained compatible, but the Mu-so 1 (which only supports AirPlay 1) has not worked automatically ever since this update. Roon is working on restoring this.
This was the update in question:
You need to do two things to make the Mu-so v1 work again apart from the question of the AirPlay code:
- Go to the Device Settings for the Mu-so in Roon, go to Advanced Settings and enable Compatibility Mode
- On an iPhone or iPad, open the Apple Home app and add the Mu-so
Hopefully this helps with the code as well. If not, maybe you can / have to turn off the AirPlay code check for the Mu-so in Apple Home.
These two steps helped in many other cases after the mentioned Roon update, like this one:
I suggest to try this first and then see about the other stuff