You have to report all of your income, no matter how little it is. There is no rule that any type of income does not have to be reported if it's under $100.
Who are "they" that say you only have to report income if it's over $100? They are either misinformed or making it up. A lot of what you see on TikTok, or any social media, is not true. No one checks it for accuracy.
If you file a tax return you have to report all of your self-employment income, even if it's less than $400. What the $400 minimum applies to is that you do not have to file a tax return if your only income for the entire year is self-employment income of less than $400.
