He Owes Me $19,000 Is Now Refusing To Pay. No Contact. Got Messages To Prove

What are my chances of lawyering up and taking this guy to court? Was a friend of mine.

He bought a business from me for $35k. Paid $16k. Got $19k to go. We agreed that he will pay the remaining by May.

It’s not may now but Since then we had a few arguments. I ended up asking him to start making small payments as I didn’t trust him anymore. He now blocked me saying I’ve been bullying him and won’t pay the remaining amount at all “no matter what you do”.

I helped him with his business, he failed it and is now refusing to pay me. Can I sue him? What are my chances of winning? I’m based in Australia.

Edited to add: I’ve got messages from him previously saying he will pay by May. But then I’ve got a recent one that says he won’t pay he anymore no matter what I do.