Is the payment form required by the prison an invoice?

It is an invoice.

According to Chinese law, when the prison requires payment, it must provide an invoice as proof of payment. An invoice is a legal financial document used to record the amount, time and related information of transactions and payments. As a legal institution, the prison needs to ensure that all payments have clear records and vouchers to ensure the legality and transparency of transactions. Providing an invoice is therefore a necessary procedure required by the prison.