Inquiry regarding paid vs. free-of-charge issuance of Purchase Confirmations

I am inquiring about the issuance of Purchase Confirmations as either paid or free-of-charge. The transaction structure consists of Company A (Korea) as the raw material supplier, Company B (Korea) as the processor and exporter, and Company C (Overseas) as the final finished goods importer. The workflow is as follows: 1) Company A supplies raw materials to Company B, and Company B performs final processing to export the finished goods to Company C. 2) Company C pays the raw material costs to Company A and the processing fees to Company B respectively. 3) Company B issues a Purchase Confirmation in relation to the export of the finished goods. 4) Based on the Purchase Confirmation, Company A issues a zero-rated tax invoice to Company B. 5) Company A issues a Certificate of Indirect Export Performance using the Purchase Confirmation, the tax invoice, and the financial transaction information of the payment received from Company C. My questions are as follows: 1. Should the Purchase Confirmation issued by Company B to Company A be in a paid or free-of-charge format? 2. Since Company A does not receive payment directly from Company B, will there be any issues with issuing the zero-rated tax invoice and obtaining the Certificate of Indirect Export Performance?