Macbook Pro M1 - iMessage/texts to non-Apple phones Error???

So I set up my new Mac M1 Max with iMessage (have an iPhone too) with my iCloud etc and it all seemed to work, even with older phones, sending a text (that don't use iPhones or iMessage)

However, had to replace the Mac for an identical M1 Max Macbook, and now iMessage doesn't send to non-Apple phones?

I have one friend who uses an ancient mobile phone, and I was texting him fine back and forth from text/iMessage via the Mac

Now when I do it, I get ''Message Send Failure' and  'Not Delivered'

What stupid thing did I do wrong? and how do I get it so that I can do ALL texts to non-Apple phones, all from my Mac and Keyboard instead of using my iPhone to type?

Thanks!