Build the backend API for a booking platform where users can browse availability, reserve a time slot, receive confirmation, and manage or cancel bookings according to business rules. The API must prevent double booking, validate all inputs, and expose clear documentation for frontend integration. The successful freelancer will be expected to work independently, share progress at agreed checkpoints, and raise questions early when a requirement needs clarification. All submitted work should be original, well organized, and ready for practical use after reasonable review.