Ask HN: What to do of non-payment by a client?

A month ago, A designer friend asked me to develop a static site for one of his client, I looked at the requirements and charged him(the client) $30 and submitted finished work with modifications the next day. I even put up his domain. All of this happened on WhatsApp.

I've been messaging me but he's just ignoring me.

I am a college student and this really bugs me. I won't do the same mistake again, I put a banner "PAY YOUR WEB DEVELOPER" on the homepage just now, waiting for him to respond.

What laws do we have to protect freelancer work, In the future what should I must do before finalizing work? Contract? Tax? Invoice?

The client was Indian and I am Indian too, I am not even expecting anything anymore but just don't want to repeat a mistake like this.