Postmen helps with Calculating Rates, generating Labels, generating Invoice and Manifests across multiple carriers.
You can add your multiple shipper accounts on Postmen and generate labels with your negotiated rates with the carrier.
You can also use the Postmen provided Shipper accounts to generate labels with Hong Kong Post.
At present Postmen can auto-import orders and fulfil orders by connecting with market places such as Shopify, Woocommerce, Opencart and Bigcommerce (https://www.postmen.com/apps).
You can also use the Postmen API to integrate Postmen with your website to calculate rates and generate labels (API documentation: https://docs.postmen.com/)
Please check Postmen Pricing at https://www.postmen.com/pricing.
You can test the Postmen features by creating an account on https://secure.postmen.com/login and using the Postmen Test Shipper accounts to calculate rates and generate labels.
You will not be charged for using the Test Shipper accounts.