Retrieves a specific coupon by its unique identifier with complete entity details.
Returns full coupon information including business rules, usage history, and current status.
Validates coupon existence and provides detailed error messages for debugging and user feedback.

This endpoint performs exact match lookup using the coupon's unique identifier.
The couponCode parameter is case-sensitive and must be an exact match.
Returns complete coupon entity including all properties, metadata, and business rule information.
Use this endpoint for detailed coupon inspection, status verification, and redemption validation.
Essential for customer service operations and troubleshooting coupon-related issues.
Remember that the couponCode cannot be null or empty.