Google assistant is not playing my daily breafing
I had the same problem as you.
This happens because of the phone's language, that doesn't support google assistant properly.  

Change your device language to English United State by navigating to Settings &gt; Languages &amp; Input &gt; Languages &gt; Add a language and then search for English United State or English US and add that language. Also, make it default language for your phone by dragging it to top from languages menu back in Settings &gt; Languages &amp; Input &gt; Languages. Then close google assistant and open again. It will work. You will find some change in its voice.

Hope it helps. :)

Source: Google forum