Unchecking, checking, and saving it and running Copy Now didn't mount the volume and gave me the error alert that the destination couldn't be found.
Looking at the drive in Disk Utility, I have:
Hard Drive
|-- Container
|----Volume 1
|----Volume 2 (this is the destination volume)
|----Volume 2 - Data (data volume created by MacOS)
__________________
:: m a t t o n e ::
|