There are three conditions for tax refund, which can be refunded if they meet.
1. VAT invoice
2. Formal customs declaration
Step 3 Recover foreign exchange
If you have paid the bill before, you can't get a tax refund. You don't have to invoice or pay in foreign exchange.
If you need commodity inspection, the import and export agency will do it for you. You just need to provide some documents and so on.