Is it permissible for an employee to take a percentage or a free travel ticket from airlines, in exchange for purchasing tickets for their company's employees?

If an employee receives their full salary, their activities and what results from them should be for the employer. It is not permissible to take money or a ticket if the company does not allow it or if it involves deception, following the prophetic prohibition against gifts to workers. However, if the company knows and permits it, or if it is customary, then there is no harm in it.