IF your total net income in a tax
year is $300 or $400, you will not owe income tax and do not have to file a return.
If you have other income that is over the threshold for owning tax, then any additional net profit (or net loss) should be included on your return, either as additional taxable income or a business loss than can reduce the tax you would otherwise owe.
CAVEAT - I AM NOT AN ACCOUNTANT and this is general information not tax or legal advice. Consult your own accountant.