Because interest expenses or income are basically based on bills that can be confirmed as the original vouchers of accounting vouchers, let alone between parent companies and wholly-owned subsidiaries.
For example, if you go to the bank for a loan, the bank will never issue an invoice when charging your interest fee, and will give you a receipt at most (whether it is transfer or cash); On the contrary, your company's money is in the bank, and when the bank pays you interest, it will never ask you to issue an invoice for it, but will give you a payment document on its own initiative.
I hope my answer can help you. Please adopt it.