You need an embassy visa for Hong Kong SAR if you have a Gambian passport
Visa options for Hong Kong SAR
Electronic visitor visa
Travelers need a visa to visit Hong Kong for Business or Tourism. A Hong Kong eVisa is the fastest and easiest way of obtaining a visa for Hong Kong because travelers can submit their application and supporting documents online. Once the application is approved, travelers receive their eVisa confirmation electronically. A valid visa is required to board the flight. If the visa is expired or doesn’t match the traveler’s passport information, travelers will not be able to board their flight.