Mostly. In most countries that I know of, either there is a limit under which you don't have to pay taxes or don't have to register a business. Perhaps your country taxes that kind of income as personal income.

And in the worst case you only risk a small fine, as the amount is small.

Much more probable is that you don't sell anything or have only a small amount of sales that no one cares about, so first check that you have a business and not a dream.

No, until that point you're not sure if you have a business service that people are willing to pay for.

And that dollar amount - you'd just pay ordinary income on it -- because it's not worth the hassle of setting up a business structure. So set aside some money from your sales to pay the taxman.