List Service Categories

Lists categories under a service (e.g. network providers for Airtime/Data, billers for Utility/Cable TV) and their serviceCategoryIds.

Path: serviceId (string, required) from List Services. Returns active categories only; an unknown serviceId returns 200 with an empty data array. isFixedAmount: true means purchases use a product from List Category Products (Data, Cable TV); false means you send your own amount (Airtime, Utility).

Error format: body validation failures (Joi) return { "status": "error", "message": "Validation error", "details": [ ... ] }; all other errors return { "success": false, "message": "..." }. Money fields (amount, fee) are Prisma Decimals and are serialized as strings (e.g. "1000").