The employee made a contract with some companies to meet his target without the knowledge of his own company
Question

I work as a booking agent for an airline. The nature of my work involves sitting in the office, and there are some tourism companies who want to make a contract with me, and I tell my company that they want to buy tickets, but my company refuses to sell to them, for fear that they will not be able to pay, or because their capital is not great. In order to meet my target, I took the booking of this company as my personal responsibility, taking on the risk that they might not be able to pay. In fact some companies were not able to pay, so I paid from my own pocket, and in return for that I keep some of the profit for myself, and I give some of it to the company that I work for. Is this halal or haram?
Praise be to Allah.The employee is an agent acting on behalf of his company when making contracts with others. If his company does not allow him to do that, then he has no right to make contracts with other companies himself, and if he makes any profit from that without the knowledge of his company, then he is consuming unlawful wealth and is betraying the trust.
Ibn Qudamah (may Allah have mercy on him) said: The agent does not have the right to do business except in the manner permitted to him by his boss, whether that was stated verbally or is assumed on the basis of custom, because he has been allowed to do business with permission, so it is limited to what he has been given permission to do. Permission is known either by a verbal statement or by custom. If the boss gives authority to a man to handle some business for him, within a specific timeframe, he does not have the authority to do business before or after that time, because his boss did not give him permission without qualification and that is not the norm according to custom."(Al-Mughni 5/251).
What you did involves two infractions:
1. Making a contract with someone with whom the company did not allow you to make a contract.
2. Making a profit from that contract without the knowledge of your company.
It makes no difference whether you give the company some of this profit or not; rather the basic principle is that all the profit should go to the company, and you have no right to anything except what was agreed upon in the contract of salary and bonuses.
Your eagerness to reach a specific target does not make it permissible for you to commit this infraction.
What you must do is repent to Allah, may He be exalted, and give that up.
You should understand that the employee is a worker who is hired to do specific tasks, and he has no right to do work during working hours for anyone except the one who hired him. So it is not permissible for him to do work for himself or anyone else during working hours, except with the permission of the company who hired him.
But if that serves a clear interest for the company, you should discuss the matter with them, and if they accept what you are doing and you are liable in the event of loss, then there is nothing wrong with it. But if they refuse, you do not have the right to do work in a manner that your company did not permit.
And Allah knows best.