Mac OS X 10.13.4 High Sierra: Messages on iCloud Grayed Out

I am using Mac OS High Sierra 10.13.4 beta 2 on my MacBook Air (13-inch, 2017). One of the new features in Mac OS X (yet to be released) is Messages on iCloud. Why is this option disabled on my computer? I would really like to be able to use feature.

Right now (this might be useful), I have three partitions on my Mac: Mac OS 10.13.3, Mac OS 10.13.4 beta 2, and Windows. Could that mean anything in regards to the situation?


PARA LA GLORIA DEL SEÑOR,

Jeremiah Yonemura