Unable to iMessage on MacBook Pro

Entering an address ( phone # or name) in the To: box works, but when a message is entered in the message box and return pressed, the address turns red and no message is sent. This is the case even when I send myself the message. I've rebooted, disabled the vpn, and kept the memory clean (as far as I can tell) of background tasks. What up the no message thing:? Is it a result of the developer beta?

Unable to iMessage on MacBook Pro
 
 
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