Basically you have to register with the authorities, but the problem is, they do not reply at all. So basically everybody just do their own thing and fly "illegally" Basic rules are; Max altitude: 40 M and you may not fly within 50 M of people, cars, roads, buildings etc. Nobody however adheres to this.
Customs will only be an issue if it is a new item that you are importing. Since yours is a "used" drone, that should not be a problem. However, having said that, this is Africa, and in Africa ANYTHING is possible.