why doesn’t messages on my computer and app sync?

When I text via my mac pro utilizing Messages it used to be in sync with my phone and other phones.

Different color thought bubbles differentiated whether it originated via the phone or via the computer. Or maybe that was whether it went through the phone company or the internet... not sure...

But now, when I text someone utilizing messages from my lap top it comes up as a new stream on the phone. The conversations are no longer seamless but now one stream originating from the phone and the other from the laptop. The phone conversation is not on the laptop and the laptop conversation not on the phone. It was once in sync. When my friend receives the message it is no longer in my original stream started via text message but now in a new one.

What did I switch off or on by accident? Why has it changed? Help me oh nerd community!!!

Signed,

Befuddled in Brooklyn.