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An invoice must include the port or merchandise destination, as this information is critical for both legal compliance and logistical purposes in international trade. The destination provides necessary details about where the goods are headed, ensuring that customs procedures can be appropriately followed, taxes and duties assessed, and that the delivery logistics are accurately coordinated. This information supports the customs clearance process by clearly indicating where the imported goods will be delivered, which is vital to both the importer and customs authorities.

While other details such as payment method, shipping company details, and authentication signatures can be important for various transactional processes, they are not universally required on all invoices for customs purposes. Their inclusion can depend on specific agreements or business practices rather than being a standard requirement. Therefore, including the destination of the merchandise is crucial for compliance and operational clarity in the context of international shipping and customs.