Is the value of refundable travel tickets a right of the state or of the employee, if the state had paid the original costs, then another party purchased new tickets due to visa circumstances, with a deduction from the per diem?

The woman asking the question should inquire with her ministry about the fate of the ticket value if it is refunded, and whether it belongs to the state or to the employee who did not utilize it. Based on the answer from the competent authority, the Shariah ruling for this value will become clear. If it belongs to the state, it must be returned. If it belongs to the employee, then it is permissible to benefit from it.