Exports against INR PO payable by Domestic Company

Transaction in GST returns: Since the goods were exported to Angola (outside India), and payment is to be received in INR from an Indian company with the consignee being a company in Angola, this transaction is considered an export. In GST returns, it should be shown as an export sale. Exports are zero-rated under GST, meaning no GST is payable on exports.

Indian Invoice in INR with/withut GST: For exports, you can raise an invoice without GST because exports are zero-rated. Since the payment is in INR from an Indian company for goods exported to Angola, you would typically issue an invoice without GST, declaring it as an export. 

Shipping Bill and RBI Compliance for inward remittance: For exports, a Shipping Bill is usually required for customs clearance. Since you have exported via AIR CARGO to Angola, you need to comply with customs procedures. For RBI compliance regarding inward remittance (payment received in INR from an Indian company for export to Angola), ensure the transaction is properly documented and reported as per RBI guidelines for export proceeds realization. The remittance should be set off in line with RBI regulations for export transactions.