What is the ruling on an individual who claimed to be a Palestinian refugee in a European country in order to obtain residency and a salary, and then it became clear that he is not, and is his salary considered lawful (halal) or unlawful (haram)?

Lying and deception are forbidden in the land of disbelief and the land of Islam. Whoever enters the land of disbelief under protection and covenant is prohibited from betraying them and taking their money through forgery and lies. If what your friend did involved forgery and deception, then it is incumbent upon him to repent and rectify his situation by adhering to the established conditions, for the Prophet, peace and blessings be upon him, said: "Muslims are bound by their conditions." If the conditions do not apply to him, then he is not entitled to anything.