iMessage not sending from MacBook Pro

Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch

https://support.apple.com/en-us/HT204681

The messages application should be relatively easy to set up for use.

Usually this works in conjunction with an iPhone, and may vary if

the Mac has older system than iDevices. Also, proximity is important.

Settings chosen within the MacOS System Preferences and iOS Settings

may or may not effect the desired outcome. I've dissimilar systems that

sometimes can't see eye-to-eye, especially after either one sees upgrade.

There may be a different article with better specific instruction for use

of the Messages and MacBook Pro. ~ With mine, iPhone was required.

If you are signed in on your Mac sign out from Messages and FaceTime power off, not a restart.

Also turn off both on your iPhone and iPad then power off.

Power on iPhone and iPad and turn both back on then sign in to both on your Mac don't rush take your time.

In case the above does not help Reset........Reset NVRAM or PRAM on your Mac - Apple Support