Is the money I received for the week of leave during my internship period unlawful gain (haram), and what should I do if it is?

The employee must fulfill the terms of the contract unless they contradict Islamic law. If the manager grants a leave that the company has not authorized him to grant, and its regulations do not permit it, then the employee is not allowed to take it, as this constitutes a breach of contract. He must return the amount he received for the duration of the leave to the company, even if by circumvention without stating the truth.