solution that worked for me:
on laptop:
open imessage app.
messages>preferences>accounts>sign out.
then sign back in. your laptop should prompt you to confirm that your laptop is now using imessage. confirm that.
imo, the key is to reconfirm imessage usage on both your iphone and mac.
on iphone:
settings>messages>text message forwarding>on
settings>messages>send&receive>...under 'you can be reached...' make sure that the email associated with icloud is selected.
once i selected my icloud email address, i received several codes on my laptop. of course those were all inactive because I sent multiple requests, which i had cancelled.
if you did the same, just cancel all codes and start over.
wifi on laptop and phone are on. lte on.