There are a number of reasons why your refund cannot be processed by the airline, which are:

• Your ticket has been used.
• You have used a part of the tickets in your booking, while the airline doesn’t allow partial refund.
• You have checked in to your flight.
• Your ticket has passed its validity period.

If one of the reasons above apply to you, your ticket, including its add-ons, will no longer be refundable.