When selling goods, other business income should be handled.
As you said, after buying products and selling them by adding software, we should establish a warehousing system like an industrial enterprise. That is to say,
Borrow: inventory materials
Taxes payable-input tax payable
Loans: bank deposits
Debit: bank deposit
Loans: other business income
Taxes payable-sales tax payable
Debit: other business costs
Lending: Inventory materials