MacBook Pro 'Failure to send' error
MacBook Pro fully updated and the date/time is correct. It won't send messages but only to certain numbers. The numbers are a mix of iPhone and non-iPhone users.
Windows, Windows 6
The article that directed you here didn't work? That's Apple definitive guidance.
If it didn't work, what exact error messages did you get?
Since you can successfully send messages, the problem may not be on your end at all. What leads you to think it's the Mac's fault?