PayPal is of the largest global payment gateway solutions. They operate in almost every country including Hong Kong. It is easy to use and set up. PayPal has a very powerful API which can be used to customise the payments based on the merchants requirement.
In Hong Kong, the most cost-efficient Payment Gateway is GoCoin with a transaction rate of 1% and no additional costs in setup fee or yearly maintenance. However, you may miss out on some of the security features like two factorPayment Gateways (Hong Kong)