Required Documents for Applying for a Local L/C (Purchase Confirmation) for Foreign Currency Acquisition

I am engaged in a trade brokerage business, selling products manufactured domestically to overseas markets. In this process, the sequence of documents is as follows: 1) Purchase Order from the overseas client, 2) Purchase Order sent to the domestic manufacturer, 3) Export Declaration Certificate, and 4) Foreign currency receipt and domestic payment. To apply for a Purchase Confirmation for foreign currency acquisition, I would like to inquire which of the items 1–3 above are required for submission, whether there are any other additional documents required, and whether the documents must be submitted as online attachments. Since this is my first time applying for a Purchase Confirmation, there is much I do not know.