You need an embassy visa for Gambia if you have a South African passport
Visa options for Gambia
Visitor visa
Travelers need a visa to visit Gambia for Business or Tourism. A paper or embassy visa is the only visa available for travelers visiting Gambia. The visa is typically a stamp or sticker added to the passport. Travelers must obtain this visa from a local embassy, consulate or visa center before traveling.
This is not offered by sherpa°.
Apply on the government site.